If 100 g of calcium carbonate on heating produces 44g of carbon dioxide, how much quicklime will be formed? Which law is followed for solving this problem?

Which law states, that in a chemical compound, elements always combine in a fixed proportion?

20g silver nitrate solution is added to 20g of sodium chloride solution. What change in mass do you expect after the reaction and why?

In a given sample of ammonia, 9g hydrogen and 42g nitrogen are present. In another sample, 5g hydrogen is present along with nitrogen. Calculate the amount of nitrogen in the second sample.

Why definition of an atom given by Dalton is no longer valid?

Why is it necessary to use the symbol for the elements?

What is wrong with the following symbols? Give the correct symbol in each case.

(i) Sodium (So)

(ii) Hydrogen (Hg)

(iii) Copper (Co)

(iv) Sulphur (S)

(v) Calcium (CA)

Name any two elements whose symbols do not start with the same letter as that of the name of the element.

Why the symbols of few elements, like sodium, do not start with the initial letter of the name?

What is the difference between 2 Cl and Cl₂? Which one of these two forms exist in nature? Also, give the atomic mass of this element.

Write the atomicity of the following:

(i) I₂ (ii) H₂S

(iii) HNO₃ (iv) Na₂SO₄

(v) S₈

An oxide of nitrogen is found to contain nitrogen and oxygen combined together in the ratio of 7: 16 by mass. Derive the formula of the oxide and name it.

How is an ion different from an atom? How is cation different from anion?

Predict the total number of atoms in each case.

(i) Calcium phosphate

(ii) Hydrogen sulphide

(iii) Magnesium bromide

(iv) Sodium oxide

(v) Aluminium hydroxide

Give symbol and valency of the following ions.

Hydroxide ion, carbonate ion.

What is the role of valency in the combination of atoms?

An element X forms X₂(CO₃)₃ type compound. What is the formula of its phosphate and chloride?

Write the formula of the following compounds.

(i) Magnesium sulphate

(ii) Sodium bromide

(iii) Calcium chloride

(iv) Potassium nitrate

(v) Sodium phosphate

How formula unit mass is different from molecular mass?

Which one is a larger quantity molar mass or molecular mass? Explain.

Calculate the molar mass of the following compounds:

(i) MgO (ii) Na₂CO₃

(iii) H₃PO₄ (iv) Ca(OH)₂

(v) Al₂(SO₄)₃

Predict the mass possessed by certain number of oxygen atoms which is equal to the number of molecules present 1g of hydrogen gas?

Calculate the number of sodium ions that are present in 212g of sodium carbonate.

Why are Dalton’s symbols not used in chemistry?

Atoms of most elements are not able to exist independently. Name two atoms which exist as independent atoms.

In which form do atoms exist in aqueous solution? Give example.

Give the symbols of the following elements.

(i) Aluminium (ii) Cobalt

(iii) Arsenic (iv) Radon

What do you understand from the statement “relative atomic mass of sulphur is 32”?

Write the ions present in

(i) Al₂(CO₃)₃ (ii) AlBr₃

An element has a valency of 3. write the simplest formula for sulphide of the element.

Name the compound represented by formula K₂SO₄.

Give the formulae of the compounds formed from the sets of carbon and oxygen.

The formula for the sulphate of a metal is MSO₄. What is the formula for the chloride of that metal?

The formula of carbonate of a metal M is M₂CO₃. What is the formula for phosphate of M?

(i) Which element is used as a standard for atomic mass scale?

(ii) What is the value of mass of this reference atom?

While searching for various atomic mass units, scientists initially took 1/16 of the mass of a naturally occurring oxygen atom as one unit. State two reasons for this.

What is the difference between 3O and O₃?

If an element X has a valency of 3, then find out the formula of its chloride and sulphide.

(i) The valency of carbon is 4 and that of chlorine is 1. What will be the formula of carbon tetrachloride?

(ii) The valency of an element X is 1 and that of oxygen is 2. What will be the formula of the compound formed by the combination of element X with oxygen?

In the chemical reaction given below, find the amount of barium sulphate formed. Also write the law involved

Name any two monovalent cations, divalent cations and trivalent cations. Also name any one compound each one of them make.

How are given mass, molar mass and number of moles related to each other?

The symbols of some of the ions are given below

Na⁺, Mg²⁺, H⁺, Cl^–, S^2–

Using this information, find out the formulae of

(i) sodium carbonate

(ii) magnesium chloride

(iii) hydrogen sulphide

Write the chemical formulae of Nitrates (NO₃^–) of Na⁺, K⁺, Al³⁺, Mg²⁺, Ca²⁺, Zn²⁺.

Write the chemical formulae and names of the compounds formed by the following ions:

(i) Cr³⁺ and SO₄^2–

(ii) Pb2+ and NO₃^–

(iii) Mg²⁺ and CO₃^2–

In a chemical compound calcium sulphate:

(i) Identify the two ions.

(ii) Write the chemical formula of compound formed when positive ion is replaced by sodium ion.

(iii) Name the resulting compound.

(i) Calculate the formula unit mass of Na₂CO₃.

[given atomic mass of Na = 23 u, C = 12 u and O = 16 u]

(ii) What is the mass of one mole of oxygen atoms?

(iii) Convert 12g of oxygen gas into mole, if atomic mass of oxygen is 16 u.

An element X has a valency 1.

(i) Write the chemical formula of its phosphide.

(ii) Write the chemical formula of its chloride.

(iii) Is element X a metal or a non-metal?

You are asked by your teacher to buy 10 moles of distilled water from a shop where small bottles each containing 20 g of such water are available. How many bottles will you buy?

State the two important laws of chemical combination. How Dalton’s atomic theory explains the two Laws?

Give a brief description of the following:

(i) Relative atomic mass

(ii) Atomic mass unit

(iii) Ions

(iv) Ionic compound

(v) Atomicity

Give the formulae of the compounds formed from the following set of elements.

(i) Carbon and hydrogen

(ii) Nitrogen and magnesium

(iii) Sodium and phosphorus

(iv) Potassium and oxygen

(v) Boron and oxygen

In an experiment, 1.288 g of barium sulphate was obtained from 1.03 g of barium. In another experiment, 3.672 g of barium sulphate gave, on reduction, 2.938 g of barium. Show that these figures verify the law of constant proportions.

Calculate the mass of each of the following:

5 moles of aluminium borate

Calculate the mass of each of the following:

2 moles of potassium bromide

Calculate the mass of each of the following:

10 moles of hydrogen cyanide

Calculate the mass of each of the following:

2 moles of methane

Calculate the mass of each of the following:

7 moles of sulphuric acid

Name a greenhouse gas with molar mass 44 g mol^–1 and is known to extinguish fire.

[Given, atomic masses of C = 12 u, O = 16 u, N_A = 6.022 × 10²³ per mole]

Name the elements present in this gas and wire their valency.

[Given, atomic masses of C = 12 u, O = 16 u, N_A = 6.022 × 10²³ per mole]

Calculate the number of moles in 360 g of this gas sample.

[Given, atomic masses of C = 12 u, O = 16 u, N_A = 6.022 × 10²³ per mole]

Calculate the number of molecules in 88 g of this gas sample.

[Given, atomic masses of C = 12 u, O = 16 u, N_A = 6.022 × 10²³ per mole]

Jyoti buys a gold jewellery which has 90% gold and the rest copper. She is given a bill which charges amount equivalent to 100% of gold. She argues with seller about the discrepancy, who settles the bill accordingly.

(i) What is the ratio of gold and copper in the jewellery?

(ii) How many atoms of gold are present in 1g of it?

(iii) What are the values displayed by Jyoti?

Iron is present in haemoglobin (in blood) which acts as oxygen carrier in our body. Deficiency of iron leads to anaemia. It must be a part of our diet.

Read the above passage and answer the following questions.

(i) Name a fruit and a green vegetable which contain iron. Is iron metal or non metal?

(ii) Give the chemical formula of iron sulphate.

(iii) How will you make students of your school aware that they must take iron in the diet regularly?

Mr. Seema taught mole concept to the students of class IX and asked the students to revise whatever had been taught. In the next period, she divided the class into several groups and asked each member of each group to explain what they have understood to the other members of their group.

Afreen a member of one of the group started to explain mole concept to the other members of her group as follow. Number of moles of molecules is equal to its mass and it is also equal to the Avogadro’s number.

Read the above passage and answer the following questions.

(i) Comment on Afreen’s understanding of mole concepts. What modification do her statement need?

(ii) What is the unit of Avogadro’s number?

(iii) What are the value displayed by Mrs. Seema?

Antacid are prescribed during acidity. Commercially available antacids consist of magnesium hydroxide [Mg(OH)₂], sugar and flavouring agents. The magnesium hydroxide act as base and form salt and water on reaction with hydrochloric acid of the stomach. The mass of salt and water formed is equal to the combined mass of

In order to verify the law of conservation of mass, we carry out chemical reactions in a closed container, so that

Which of the following represents a correct chemical formula? Name it.

Four students A, B, C and D verified the law of conservation of mass by performing chemical reaction between barium chloride and sodium sulphate. All of them took 107.2 g barium chloride solution and 116.1g of sodium sulphate solution and mixed them in the beaker of mass 150 g. They reported their results as follows:

The correct observation is that of student.

In a chemical reaction 10.6 g of sodium carbonate reacted with 12g of ethanoic acid. The products were 4.4 g carbon dioxide, 1.8 g of water and sodium ethanoate. The mass of sodium ethanoate formed is

During an experiment hydrogen (H₂) and oxygen (O₂) gases reacted in an electric are to produce water as

follows: 2H + O₂ 2H₂O

The experiment is repeated three times and data tabulated as shown below:

During 3^rd experiment the researcher forgot to list masses of H₂ and O₂ used. So, if the law of constant proportion is correct then find mass of O₂ used during 3^rd experiment.

Nitrogen and hydrogen combine together to form ammonia.

N₂ + 3H₂→ 2NH₃

[Relative atomic masses of N = 14 u, H = 1 u]

The mass of nitrogen and hydrogen which combine together to form 6.8 g ammonia is

Which of the following correctly represent 360 g of water?

I. 2 moles of H₂O

II. 20 moles of water

III. 6.022 × 10²³ molecules of water

IV. 1.2044 × 10²⁵ molecules of water

3.42 g of glucose are dissolved in 18 g of water in a beaker. The number of oxygen atoms in the solution is

Which of the following contains maximum number of molecules?