Mass of 1 g of element X = 2 x 10 -23 g, Mass of 1 mole of element X = 2 x 10-23 x 6.022 x 1023 = 12.044 g, Molar mass of the element X = mass of 1 mole of element = 12 u, Verify your number to create your account, Sign up with different email address/mobile number, NEWSLETTER : Get latest updates in your inbox, Need assistance? For example- A molecule of hydrogen element consists of 2 hydrogen atoms combined together. 3. Give two examples of each type of compounds. Phosphorus (f) Sodium. How many grams of magnesium will have the same number of atoms as 6 grams of carbon? What is the mass of 5 moles of sodium carbonate (Na2CO3)? per mole of a substance. (b) In what form do noble gases occur in nature? (a) Give two symbols which have been derived from the ‘English names’ of the elements. Atomic masses : Na =23 u ; O=16 u; Al = 27 u), (a).Molecular of moles = For ex. (a)  Postulates of Dalton’s atomic theory:       1)  All the matter is made up of very small particles called ‘atoms’. How much is the gram molecular mass of oxygen ? There are as many kinds of atoms as are elements. of protons (11) + No. It also represents 12 gms of Carbon. neutrons? (b). iii. (a) Name (i) liquid X, (ii) gas Y and (iii) gas Z. State whether the following statement is true or false: False, the symbol of element cobalt is Co and CO is carbon monoxide. Kanad was one of the first person to propose that matter is made up of particles called ‘parmanu’. Is it possible to see atoms these days? Here again, one can see that 1.25 equivalent of CuO decomposed to form 1 equivalent of Cu and 0.25 equivalent of oxygen. (a). As valency of element A is 5 and valency of chlorine is -1. As valency of Mg is +2 and that of X is -2 so the formula of Magnesium salt of X will be MgX. Elements present are Sulphur and Oxygen. (b) What b) A molecule is an electrically neutral group of two or more atoms chemically bonded together. C.01] Quick Links. obtained'. Give one example to illustrate this law. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds.After hydrogen and helium, oxygen is the third-most abundant element in the universe by mass. 17. For ex. The radius of an atom is usually expressed in ‘nanometres’. ... Now since equal moles of all the substances contain equal number of atoms so, 1/32 mole of oxygen will also contain x atoms like S. 16 g of oxygen = 1 mole. The mass of one molecule of a substance is 4.65 x 10-23 g. What is its molecular mass? So, 4 moles of nitrogen and 4 moles of oxygen contains same no. 29. (i) Ozone molecule, O3 (ii) Ethanoic acid, CH3COOH. masses: H = 1 u, S = 32 u, C = 12 u), (a).Molecular formed by the gain of one or more electrons by an atom. Yes, with the help of advanced technologies we can see atoms by using electronic microscopes. (d) The law of conservation of mass is followed, i.e. One mole represents the amount of a substance equal to its 'GRAM ATOMIC MASS' or 'GRAM MOLECULAR MASS' and 6.022 x 1023 no. Now since equal moles of all the substances contain equal number of atoms so, 1/32 mole of oxygen will also contain x atoms like S. Now, 1/32 mole of oxygen contains = x atoms, So, 1/16 mole of oxygen will contain = x x 32/16 = 2x atoms. The Calculate the molecular mass of chloroform(CHCl3). It represents one atom of Hydrogen element. Write down the formulae for the following compounds: (a) Calcium oxide (b) Magnesium hydroxide. of moles of nitrogen = 56g/14g = 4 moles. Atoms of the same elements can combine in more than one ratio to form more than one compound. Diagram 2, because it shows the formation of a hydrogen bond between an H atom bonded to an O atom with an O atom from another molecule. (b) An element Y has a valency of 4. What is the formula unit of (, Formula unit of magnesium chloride - MgCl, So, the formula of chloride of A is ACl, The Gas Y is produced at the positive electrode whereas gas Z is obtained at the negative electrode. Copper sulphate reacts with sodium hydroxide to form a blue precipitate of copper hydroxide and sodium sulphate. No. If 100 gms of calcium carbonate is decomposed completely, then 56 gms of calcium oxide and 44 gms of carbon dioxide are formed. H2O also represents Define ‘molecular mass’ of a substance. On adding a few drops of dilute hydrochloric acid to P, brisk effervescence, Anions are (e) Which law of chemical combination is illustrated by the example given in this problem? Y (NO3)4. A liquid compound X of molecular mass 18 u can be obtained from a number of natural sources. Write the formulae of its two oxides. two symbols which have been derived from the 'English names' of the elements. Calculate its molecular mass. (a) Water (b) Ammonia (c) Methane (d) Sulphur dioxide (e) Ethanol. What name was given by him to these particles? the significance of the formula of H2O? Elements present are carbon, hydrogen and oxygen. (a) Give  iii. to form Mg+2. Which law of chemical combination is illustrated by this data? formed by the gain of one or more electrons by an atom. h) During chemical combination, atoms of different elements combine in small whole numbers to form compounds. Contact us on below numbers, How many moles are represented by 100 g of glucose, C6H12O6? For example, water, H 2 O, and hydrogen peroxide, H 2 O 2, are alike in that their respective molecules are composed of hydrogen and oxygen atoms. 22. (d).Sulphur dioxide-SO2; Elements present are Sulphur and Oxygen. 44. (b) The atomic mass of an element is the relative mass of its atom as compared with the mass of a carbon-12 atom taken as 12 units. What are ; (b). (a) What How is the size of an atom indicated? (e).Ethanol-C2H5OH; Elements present are carbon, hydrogen and oxygen. (a). So, chemical formula of ammonia is NH3. S is one atom of sulphur and O4 is four atoms of oxygen. total mass of reactants = (15.95 gm + 8 gm) = 23.95 gm, total mass of products = (9.75 gm + 14.2 gm) = 23.95 gm. of oxide of Z ? John Dalton is the scientist who gave atomic theory of matter.       8) During chemical combination, atoms of different elements combine in small whole numbers to form compounds. The radius of an atom is usually expressed, The major drawback of Dalton's atomic theory is that. ), the same masses of hydrogen and oxygen elements are obtained in each case. 41. Which of the following contains maximum number of molecules? For Ex. (b) Which postulate of Dalton’s atomic theory can explain the law of conservation of mass? (b) What will be the number of (i) protons (ii) electrons, and (iii) neutrons, in the ion formed from X? Given mass / Molar mass = 12g /32g = 0.375. Name the unit in which the radius of an atom is usually expressed. The elements consist of atoms having fixed mass, and that the number and kind of atoms of each element in a given compound is fixed. Water is made = 0.1 moles. (a) In what form does oxygen gas occur in nature? State Water- H2O; Elements present are Hydrogen and Oxygen. (Atomic masses: C = 12 u; H = 1 u; Cl = 35.5 u), Molecular mass of chloroform (CHCl3) = 1 x C + 1 x H + 3 x Cl. The law of conservation of mass was given by: 64. Thus, 10g of O2 contains more no. atoms were thought to be indivisible. 72, 505 (1995) Multipoles and Symmetry Formula also represents one mole 4. Calculate the molecular mass of ethanoic acid, CH3COOH. Mercury, Silver. YCl4 (ii). Name the unit in which the radius of an atom is usually expressed. Chemical formula of sulphur dioxide is SO2. 1.5 moles of Na2SO3 has 3 moles of Na, 1.5 mole of S and 4.5 moles of O. So, 0.17 mole of H2S will weigh = 34 x 0.17 g = 5.78 g. Show by means of calculations that 5 moles of CO2 and 5 moles of H2O do not have the same mass. HCl and H2S. 1. An One molecule of argon  comprises only one atom and therefore the atomicity of argon is one. Out of ozone, phosphorus, sulphur and krypton, the elements having the lowest and highest atomicities are respectively: 69. They exist in combined form i.e in the form of molecules and ions. (b) Explain the significance of the symbol H. (a).Significance of symbol of element -. laws of chemical combination. Calculate the molecular masses of the following compounds: (a). not possible to see an atom even with the most powerful microscope? Molecular mass of Ethyne (C2H2) = 2 x 12 + 2 x 1 = 26 u. How much is the gram atomic mass of oxygen? 53. a) State the various postulates of Dalton’s atomic theory of matter. (a) One atomic mass unit is defined as exactly one-twelfth the mass of an atom of carbon-12. The symbol of element is the "first letter" or "first letter and another letter" of the English name or Latin name of the element. formula of carbonate of a metal M is M. (a). They are an electrically neutral group of two or more atoms chemically bond together. ‘If 100 grams of calcium carbonate(whether in the form of marble or chalk) are decomposed completely, then 56 grams of calcium oxide and 44 grams of carbon dioxide are obtained’. 55. How many (a). Give reasons for your answer. If one mole of nitrogen molecules weighs 28 g, calculate the mass of one molecule of nitrogen in grams. (a) One atomic mass unit is defined as exactly one-twelfth the mass of an atom of carbon-12. Hence, mass of 4 mole of oxygen = 4 x 16g = 64 g, What mass of nitrogen, N2, will contain the same number of molecules as 1.8 g of water, H2O? The major drawback of Dalton's atomic theory is that atoms were thought to be indivisible. For example: 100gs of calcium carbonate decomposes to produce 56gms of calcium oxide and 44gms of carbon dioxide. So, 100 g of glucose will have = 1 x 100/180 = 0.55 moles. Explain with an example. Which part of the Dalton’s atomic theory came from the law of constant proportions given by Proust? No, the statement is not valid because atoms can be divided into subatomic particles called electrons, protons and neutrons. a substance. The was given by Proust. Molecular mass of ethane (C2H4) = 2 x 12 + 4 x 1 = 28 u, (d). Calculate the number of molecules in 4 g of oxygen.       6) Atoms of different elements differ in mass, size and chemical properties. Molecular A change in the physical state can be brought about (a) only when energy is given to the system Now, when 5 gm of calcium is burnt in 20 gm of oxygen, then also 7gm of calcium oxide will be formed because chemical reactions follows law of constant proportion. H2 represents one molecule of hydrogen which is formed by the bonding of two separate hydrogen atoms. State the law of conservation of mass. [c]. (b) What weight of each element is present in 1.5 moles of sodium sulphite, Na2SO3? (e) Law of conservation of mass is illustrated by the example. 21. Chemical formula of element – O2 for hydrogen, Chemical formula of compound – CO2 for water. 4. 32 g of oxygen (1 mole of oxygen) has = 6.022 x 1023 molecules of oxygen. of moles of SO2 = 10g/64g = 0.15, Total no. Which of the following has maximum number of atoms? Formula unit of magnesium chloride - MgCl2, (i). Atoms can neither be created nor destroyed. electrons than the normal atoms? Diagram 1, because it shows strong, directional dipole-dipole forces between two polar ethanol molecules. 54. Work out the formula for magnesium hydrogen carbonate. Thus, the number of moles of H2 that were used = 1/2(number of moles of HCl that were formed) = 1/2(12.0) = 6.0 moles. (e) 64 of oxygen gas contains _______ moles of oxygen atoms. represents two atoms of hydrogen, one atom of sulphur What do (a) Define 'formula unit' of an ionic compound. will be the formula of its phosphate? of atoms as compared to 50g of Fe. How much is the difference in their masses? 40. If the valency of hydrogen is 1 and that of nitrogen is 3, work out formula for ammonia. Name the scientist who gave atomic theory of matter. Educ. For example: When calcium carbonate is heated, a chemical reaction takes place to form calcium oxide and calcium carbonate. a substance. substance. dioxide are obtained'. c) The molecule of an element contains two or more similar atoms chemically bonded together. Hence, mass of 0.1 mole of nitrogen = 0.1 x 28 g = 2.8 g, If one gram of sulphur contains x atoms, calculate the number of atoms in one gram of oxygen element (Atomic masses: S = 32 u; O = 16 u). (a). The molar mass of the substance is the mass of 1 mole of that substance. Antonie Lavoisier proposed the Law of conservation of mass which states that ‘Mass can be neither created nor destroyed’ so in a chemical reaction, the total mass of reactants must be equal to the total mass of products. Write the simplest formula for: As valency of bromine is -1 and that of element X is +2 so, the resulting compound is XBr2. The elements consist of atoms having fixed mass, and that the number and kind of atoms of each element in a given compound is fixed. 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Magnesium loses 2 electron (b) Formula also represents one mole Different atoms and molecules have different properties, thus the properties of matter depend on properties of atoms and molecules which it is made. Thus, 50g of Al has more no. the significance of the formula of H, Calculate the molecular mass of Nitric acid, HNO, Calculate the molecular mass of hydrogen bromide (, (b). State whether the following statements are true or false: (a) A sodium ion has positive charge because it has more protons than a neutral atom. However, because a hydrogen peroxide molecule contains two oxygen atoms, as opposed to the water molecule, which has only one, the two substances exhibit very different properties. Percent composition can also tell you about the different elements present in an ionic compound as well.. Let's look at two examples. Name and formula of the resulting compound is Carbon disulphide; CS2. Molecular compounds- These compounds are formed by the combination between two non-metal elements. (a) Name the element used as a standard for atomic mass scale. Which part of the Dalton's atomic theory came from the law of constant proportions given by Proust? Anion will be formed by element X ; Symbol : What name is given to the amount of substance containing 6.022 x 10, What name It means, a pure chemical compound is always made up of the same elements in the same percentage. (d) A potassium ion has positive charge because it contains less _____ than _____. Formula gives the number of atoms - C represents one atom of the element Carbon. So, 0.1 moles of water and 0.1 moles of nitrogen contains same no. a) An atom is the smallest particle of an element that can take part in a chemical reaction. Law of ii. What is 71. H2 : It is a covalent molecule. Law of conservation of mass by LAVOISIER states that: "Mass can neither be created nor be destroyed in a chemical reaction". What does the symbol 'nm' represent? [b]. It represents a definite mass of the element. relation between nanometer and meter. (a) What is meant by the 'molar mass' of a substance? For example- The molecule of hydrogen chloride(. (i). Explain with two examples. What does the symbol ‘nm’ represent? 57. Law of chemical combination is one of the concepts came forward that comprises of three laws. 34. formula of The molecule of an element contains two or more similar atoms chemically bonded together. Atoms of different elements differ in mass, size and chemical properties. Your email address will not be published. They are always combined together in the same constant proportion of 11:89 or 1:8 by mass. (a). (a) 1 mole contains _______ atoms, molecules or ions of a substance. State the law of constant proportions. 48. (c) What is meant by saying that ‘the atomic mass of oxygen is 16’? (c) What type of ion will be formed by an atom of element Y? iii. (b) 1 mole of aluminium weighing 27g has = 6.022 x 1023 atoms of Al, So, 1g of Al has = 0.22 x 1023 atoms of Al, Hence, 50g of Al will have = 50 x 0.22 x 1023 atoms of Al, 1 mole of iron weighing 56g has = 6.022 x 1023 atoms of Fe, So, 1g of Fe has = 0.10 x 1023 atoms of Fe, Hence, 50g of Fe will have = 50 x 0.10 x 1023 atoms of Fe = 5 x 1023 atoms of Fe. elements represented by the following symbols: What is meant by atomicity? What is meant by the symbol of an element? What are the two things that a mole represents. An anion is 1. of This chapter deals mainly deals with the origin of atom and molecules and the various concepts of atoms, laws, and theories based on it. Formula represents one molecule of Fill in the following blanks with suitable words: (a) In water, the proportion of oxygen and hydrogen is _____ by mass. 24. Gas Y (oxygen) is necessary for breathing. NaCl : Na+ (cation) and Cl- (anion). The postulate "The elements consist of atoms having fixed mass, and that the number and kind of atoms of each element in a given compound is fixed" can be used to explain the law of constant proportions. (a) Carbon is used as a standard for atomic mass scale. (a) What is 25. The atomicities of ozone, sulphur, phosphorus and argon are respectively: 58. According to How do atoms usually exist ? molecular formula of glucose is C6H12O6. (a) Oxygen gas occurs as a diatomic molecule in nature. So, 0.5 moles of carbon and 0.5 moles of magnesium contains same no. Oxygen is the chemical element with the symbol O and atomic number 8. Hence, mass of 0.5 mole of magnesium = 0.5 x 24g = 12g. 9. Formula Mass of Sodium carbonate (Na2CO3) = 2xNa + 1xC + 3xO= (2x23 + 1x12 + 3x16) u = 106 u. 10. The atoms of which of the following pair of elements are most likely to exist in free state? (c) Which postulate of Dalton’s atomic theory can explain the law of constant proportions?Â. Explain Law of constant proportion given by PROUST states that "A chemical compound always consists of the same elements combined together in the same proportion by mass.". (c) What is the difference between the molecule of an element and the molecule of a compound? 3. Molecular mass of methane (CH4) = 12 + 4 = 16 u, (b). 42. They usually exist in combination with the atoms of same element or another element. Is it possible to see atoms these days? (b) Noble gases occur as monoatomic gases in nature. On adding a few drops of dilute hydrochloric acid to P, brisk effervescence are produced. Hence, law of constant proportion is verified. What weight of oxygen gas will contain the same number of molecules as 56 g of nitrogen gas ? When an electric current is passed through 200 grams of pure liquid X under suitable conditions, then 178 grams of gas Y and 22 grams of gas Z are produced. is given to the number 6.022 X 1023? of each element present in one molecule. (c) Which postulate of Dalton's atomic theory can explain the law of constant proportions? of molecules. Give one major drawback of Dalton’s atomic theory of matter. (b) Total mass of Q and R = 22gm + 28gm = 50gm. the numerical value of Avogadro number? Avogadro’s number is a proportion that relates molar mass on an atomic scale to physical mass on a human scale. Which was given So, in a chemical reaction, the total mass of reactants must be equal to the total mass of products. (a) What is an atom? names and symbols of five familiar substances which you think are elements. 39. [G16 Rev. What is its symbol? two symbols which have been derived from the 'Latin names' of the elements. Atoms are of various kinds. 2N represents two atom of nitrogen which are not chemically bonded. 2H represents two separate atoms of hydrogen. and four atoms of oxygen. (f) What could the elements X and Y be? (a). Explain with examples. Diagram 1, because it shows hydrogen bonds forming between hydrogen atoms from different ethanol molecules. Which postulate of Dalton’s atomic theory is the result of law of conservation of mass given by Lavoisier? chemical reaction, the sum of the masses of the reactants and the products Work out the formulae for the following compounds : Thus, the formula of sodium oxide is Na2O. In water, the proportion of oxygen and hydrogen by mass is: 73.