Question:
Magnesium and oxygen combine in the ratio of 3 : 2 by mass to form magnesium oxide. How much oxygen is required to react completely with 12 g of magnesium?
Answer:
Magnesium (Mg) and Oxygen (O) combine in the ratio = 3:2 to form compound magnesium oxide (MgO). It follows Law of Constant proportions.
⇒ 3g of Mg combines with = 2g of O.
∴ 12g of Mg combines with = 2 × 12/3 = 8g of O.
Atoms and Molecules
Q 1.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 2.
What is gram-atomic mass of an element?
Q 3.
Define 'formula mass' of a compound.
Q 4.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 5.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 6.
(a) Define gram atomic mass of a substance.How much is the gram atomic mass of oxygen ?
(b) How many moles of oxygen atoms are present in one mole of the following compounds ?
(i)Al
(ii) co
2(iii) C1
(iv) H
(p)A1
Q 7.
Show by means of calculations that 5 moles of CO, and 5 moles of H
do not have the same mass. How much is the difference in their masses ?
Q 8.
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
(b)A chloride ion has negative charge because it has more electrons than a neutral atom.
Q 9.
Work out the formulae for the following compounds :
(a) Sodium oxide
Q 10.
What are the building blocks of matter ?
Q 11.
The molecular formula of glucose is C
Q 12.
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
Q 13.
How many moles of calcium carbonate (CaCO
Q 14.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 15.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 16.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 17.
Fill in the blanks:
Hydrogen and oxygen combines to form H
2O and H
2O
2. These two compounds obey the law of ____________________.
Q 19.
Who introduced the term 'mole' in chemistry?
Q 20.
Name the unit in which the radius of an atom is usually expressed.
Q 21.
Is it possible to see atoms these days ? Explain your answer.
Q 22.
Fill in the following blanks :
(a)1 mole Contains...........atoms- molecules or ions of a substance
(b)A mole represents an..........number of Particles of a substance.
(c)60 g of carbon element are...........moles of carbon atoms.
(d) 0.5 mole of calcium element has a mass of..........
(e) 64 g of oxygen gas contains..........moles of oxygen atoms.
Q 23.
Calculate the mass m grams of 0.17 mole of hydrogen sulphide, H,S.(Atomic masses : H = 1 U/ S = 32 u)
Q 24.
Calculate the mole ratio of 240 g of calcium and 240 g of magnesium. (Ca = 40 u ; Mg = 24 u)
Q 25.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 26.
Fill in the blanks:
The _______________ of a compound is a symbolic representation of its composition.
Q 27.
Which of the following statements is NOT true about an atom?
(a) Atoms are the building blocks from which molecules and ions are formed.
(b) Atoms cannot exist independently.
(c) Atoms are neutral in nature
(d) Atoms combine together to form matter that we can see, feel or touch.
Q 28.
What is the chemical symbol for iron?
Q 29.
What is valency of an element?
Q 30.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 31.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 32.
'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'.Which law of chemical combination is illustrated by this statement ?
Q 33.
Calculate the molecular mass of hydrogen bromide (HBr).
(Atomic masses: H=1; Br= 80 U)
Q 34.
What are (ionic compounds, and (ii) molecular compounds ? Give two examples of each type of compounds.
Q 35.
What is the difference between a cation and an anion ? Explain with examples. Using this information, write down the formulae of:
(i) Sodium sulphide
(ii) Copper nitrate
Q 36.
How many atoms are present in one gram atomic mass of a substance ?
Q 37.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 38.
How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)
Q 39.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 40.
If 12 g of carbon is burnt in the presence of 32 g of oxygen, how much carbon dioxide will be formed?
Q 41.
What are the postulates of Dalton's atomic theory?
Q 42.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 43.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 44.
Fill in the blanks:
_________ are building block of all matter.
Q 45.
Who proposed the chemical notation based on first two letters of the name of the element?
Q 46.
How will you define chemical symbol?
Q 47.
Fill in the blanks:
According to Dalton's atomic theory, atoms of different elements differ in ______, size and chemical properties.
Q 48.
Fill in the blanks:
____________ is formed by the loss of one or more electrons by an atom.
Q 49.
Calculate the formula unit masses of ZnO, Na
2O, K
2CO
3, given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u, C = 12 u, and O = 16 u.
Q 50.
How do we know the presence of atoms if they do not exist independently for most of the elements?
