ICSE std 7 chemistry ch1 test

Question 1 of 21

Which of the following statements represents the law of conservation of mass?

CHEMISTRY TestCh-1 Elements and Compounds

60 minutes

Question 2 of 21

Use the following information to answer the next question.

In a chemical reaction, x g of silver nitrate (AgNO3) reacts with 7.3 g of hydrochloric acid (HCl) to produce 28.7 g of silver chloride (AgCl) and 12.6 g of nitric acid (HNO3) [Atomic mass of Ag = 108 u, Cl = 35.5 u, N = 14 u, O = 16 u].

What is the value of x?

A.Atoms of a given element are identical in mass.

B.Atoms of different elements have different masses.

C.Mass can neither be created nor destroyed in a chemical reaction.

D. In a chemical substance, elements are always present in definite proportions by mass.

A.17 g

B.17.5 g

C.34 g

D.34.5 g

1

Question 3 of 21

Use the following information to answer the next question.

The ratio by mass of carbon and oxygen in carbon dioxide is 3:8.

The respective masses of carbon and oxygen required to react completely to form 33 g of carbon dioxide are

Question 4 of 21

Which of the following symbols is approved by the IUPAC for copper?

Question 5 of 21

Which of the following elements has atomicity 2?

A.9 g and 24 g

B.12 g and 21 g

C.21 g and 12 g

D.24 g and 9 g

A.Ca

B.Co

C.Cu

D.Cl

A.Helium

B.Nitrogen

C.Aluminium

D.Phosphorus

2

Question 6 of 21

The ratio by mass of atoms for sodium oxide is

Question 7 of 21

The ratio by the number of atoms for aluminium oxide is

Question 8 of 21

Which of the following ions is mono-atomic?

Question 9 of 21

A.Na:O = 8:23

B.Na:O = 16:23

C.O:Na = 16:23

D.O:Na = 8:23

A.Al:O = 1:2

B.Al:O = 1:3

C.Al:O = 2:3

D.Al:O = 3:2

A.Nitrate

B.Sulphite

C.Sulphide

D.Hydroxide

3

What is the chemical formula of sodium carbonate?

Question 10 of 21

The molecular mass of calcium hydroxide is

Question 11 of 21

Which of the following compounds has a molecular mass equal to 95 u?

Question 12 of 21

A.NaCO3

B.Na2CO3

C.Na(CO3)2

D.Na3(CO3)2

A.57 u

B.58 u

C.74 u

D.97 u

A.Sodium nitrate

B.Carbon disulphide

C.Calcium hydroxide

D.Magnesium chloride

4

The formula unit mass of potassium chloride is

Question 13 of 21

Use the following information to answer the next question.

Protons are , whereas neutrons are .

The information inwhich alternative completes the given statement?

Question 14 of 21

A.74.5 u

B.59.0 u

C.113.5 u

D.110.0 u

A.i ii

positively charged neutral

B.i ii

neutral negatively charged

C.i ii

negatively charged positively charged

D.i ii

positively charged negatively charged

5

In which of the following situations, an atom would have a positive charge?

Question 15 of 21

Use the following information to answer the next question.

An atom of an element ‘X’ has 7 protons and has a mass number of 14 u.

How many neutrons are present in the atom of ‘X’?

Question 16 of 21

Use the following information to answer the next question.

The given figure shows a schematic atomic structure of a neutral atom.

A.Number of protons = 1, number of electrons = 1

B.Number of protons = 1, number of electrons = 2

C.Number of protons = 2, number of electrons = 1

D.Number of protons = 2, number of electrons = 2

A.21

B.10

C.7

D.0

6

Which of the following elements is represented by the given structure?

Question 17 of 21

Which of the following species is not an isotope of hydrogen?

Question 18 of 21

The fuel used in nuclear reactions is an isotope of

Question 19 of 21An atom is positively charged if it has

A.Boron

B.Nitrogen

C.Aluminium

D.Phosphorus

A.

B.

C.

D.

A.hydrogen

B.uranium

C.cobalt

D.iodine

7

Question 20 of 21

Use the following information to answer the next question.

A neutral element X has 10 electrons and 12 neutrons in its atom.

The atomic number of element X is

Question 21 of 21

Neutron is absent from the nucleus of an atom of

A.number of protons = 7, number of electrons = 8, number of neutrons = 8

B. number of protons = 9, number of electrons = 9, number of neutrons = 10

C.number of protons = 8, number of electrons = 7, number of neutrons = 9

D.number of protons = 6, number of electrons = 8, number of neutrons = 6

A.10

B.12

C.20

D.22

A.boron

B.lithium

C.hydrogen

D.phosphorus

8

Answers1-c2-c3-a4-c5-b6-d7-c8-c9-b10-c11-d12-a13-a14-c15-c16-d17-d18-b19-c20-a21-c

9

Solutions

1

The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. Thus, the total mass before a reaction is equal to the total mass after the reaction.

The correct answer is C.

Why your answer is incorrect

According to Dalton’s atomic theory, atoms of a given element are identical in mass and atoms of different elements have different masses.

2

According to the law of conservation of mass, the total mass before a reaction is equal to the total mass after the reaction.

Therefore,

Mass of AgNO3 + Mass of HCl = Mass of AgCl + Mass of HNO3

⇒ x + 7.3 = 28.7 + 12.6

⇒ x = (28.7 + 12.6) − 7.3

= 34 g

The correct answer is C.

3

t is given that the ratio by mass of carbon and oxygen in carbon dioxide is 3:8.

Let the required mass of carbon and oxygen be 3x g and 8x g respectively.

Now, 3x + 8x = 33

11⇒ x = 33

⇒ x = 3

Therefore, the required mass of carbon = 3 × 3 g

10

= 9 g

And, the required mass of oxygen = 8 × 3 g

= 24 g

The correct answer is A.

4

The IUPAC approves the symbol Cu for copper.

The correct answer is C.

5

The number of atoms constituting a molecule is known as its atomicity. A molecule of nitrogen molecule consists of two atoms of nitrogen. Hence, it is a diatomic molecule and its atomicity is 2.

The correct answer is B.

6

A molecule of sodium oxide (Na2O) consists of one oxygen (O) and two sodium (Na) atoms.

Atomic mass of Na = 23 u

Atomic mass of O = 16 u

Thus, the ratio by mass of atoms for Na2O can be calculated as:

Na:O = 2 × 23 : 1 × 16

= 46:16

= 23:8

Or, O:Na = 8:23

The correct answer is D.

7

11

A molecule of aluminium oxide (Al2O3) consists of two aluminium atoms and three oxygen atoms. Therefore, the ratio by the number of atoms for Al2O3 is

Al:O = 2:3.

The correct answer is C.

8

Sulphide (S2−) ion is mono-atomic since it consists of only one single charged atom.

The correct answer is C.

9

The symbols for sodium and carbonate ions are Na+ and respectively.

To write the chemical formula of the given compound, the constituent particles and their charges are written as shown in the figure. Then, by crossing over the charges of the combining particles, we get

Thus, the chemical formula of sodium carbonate is Na2CO3.

The correct answer is B.

10

The chemical formula of calcium hydroxide is Ca(OH)2.

We know that,

Atomic mass of calcium (Ca) = 40 u

Atomic mass of oxygen (O) = 16 u

Atomic mass of hydrogen (H) = 1 u

12

Molecular mass of any substance is the sum of the atomic masses of all atoms in a molecule of that substance.

Thus, the molecular mass of Ca(OH)2

= 1× atomic mass of Ca + 2× atomic mass of O + 2× atomic mass of hydrogen

= 1 × 40 + 2 × 16 + 2 × 1

= 40 + 32 + 2

= 74 u

Hence, the molecular mass of calcium hydroxide is 74 u.

The correct answer is C.

11

The molecular mass of any substance is the sum of the atomic masses of all atoms in a molecule of that substance.

Molecular mass of magnesium chloride (MgCl2)

= 1 × Atomic mass of Mg + 2 × Atomic mass of Cl

= 1 × 24 + 2 × 35.5

= 24 + 71

= 95 u

The correct answer is D.

12

Calculation of the formula unit mass is done in the same manner as that of the calculation of molecular mass. The formula unit mass of a substance is the sum of atomic masses of all atoms in a formula unit of that compound.

The chemical formula of potassium chloride is KCl.

Atomic mass of potassium (K) = 39 u

13

Atomic mass of chlorine (Cl) = 35.5 u

Thus, formula unit mass of potassium chloride (KCl)

= 1 × atomic mass of K + 1 × atomic mass of Cl

= 1 × 39 u + 1 × 35.5 u

= (39 + 35.5) u

= 74.5 u

The correct answer is A.

13

Protons are subatomic particles that are positively charged. Neutrons are also sub-atomic particles that carry no charge. Hence, neutrons are neutral.

The correct answer is A.

14

Protons and electrons have charge equal in magnitude but opposite in sign. Protons are positively charged and electrons are negatively charged. When the number of protons of an atom is more than the number of its electrons, then the atom is positively charged. Hence, an atom containing two protons and one electron is positively charged.

The correct answer is C.

15

The mass number of an atom is the sum of the number of all the protons and neutrons present in that atom.

Number of protons = 7 (given)

Thus, the number of neutrons = 14 − 7 = 7

The correct answer is C.

16

A neutral atom contains an equal number of protons and electrons. The given figure shows that the atom contains 15 electrons. Thus, the number of protons present in the atom is 15. The number of protons present in an atom represents the atomic number of

14

the element. Thus, the atomic number of the given atom is 15, which represents the atomic number of phosphorus. Hence, the given figure represents the scematic atomic structure of phosphorus.

The correct answer is D.

17

Isotopes are atoms of the same element having the same atomic number, but a different mass number.

Hydrogen has three isotopes. They are protium , deuterium , and tritium .

does not exist.

The correct answer is D.

18

An isotope of uranium is used as a fuel in nuclear reactors.

The correct answer is B.

19

Neutrons are neutral. Thus, the charge of an atom does not depend upon the number of neutrons it has. It depends upon the number of protons and electrons the atom has.

The charges on a proton and on an electron are equal in magnitude, but opposite in sign. Protons are positively charged and electrons are negatively charged. Thus, if the number of protons is more than that of electrons in an atom, then the atom would be positively charged. Similarly, if the number of protons is less than that of electrons, then the atom would be negatively charged. On the other hand, if the number of protons and electrons are equal in an atom, then the atom would be neutral.

Hence, the atom having 8 protons and 7 electrons will be positively charged.

The correct answer is C.

20

In a neutral atom, the numbers of protons and electrons are equal. Therefore, the atom of element X contains 10 protons.

15

The atomic number of an element is the number of protons present in the atom of that element.

Therefore, the atomic number of element X is 10.

The correct answer is A.

21

In the nucleus of hydrogen, only one proton is present. There is no neutron present in the nucleus of a hydrogen atom.

The correct answer is C.

16