N5 Chemistry MC 2017

In a reaction, the mass lost in 30 seconds was 2 g.

What is the average rate of reaction, in g s⁻¹, over this time?

An atom has 21 protons, 21 electrons and 24 neutrons.

The atom has

• atomic number 24 and mass number 42

• atomic number 45 and mass number 21

• atomic number 21 and mass number 45

• atomic number 24 and mass number 45

Answer explanation

Atomic number = no of protons = 21 and mass no.= protons+neutrons = 21+24 = 45

What is the charge on the zinc ion in zinc dichromate, ZnCr₂O₇?

You may wish to use the data booklet to help you.

• 2+

• 2-

• 1+

• 1-

Answer explanation

Dichromate ion formula is Cr₂O₇^2- - Cr₂O₇^2- ion must be balanced by a 2⁺ ion, so Zn²⁺

The table contains information about magnesium and magnesium chloride. When molten magnesium chloride is electrolysed at 730 °C the magnesium appears as a

• solid on the surface of the molten magnesium chloride

• solid at the bottom of the molten magnesium chloride

• liquid at the bottom of the molten magnesium chloride

• liquid on the surface of the molten magnesium chloride

Answer explanation

A Magnesium melts at 650^oC - temperature is 730^oC so magnesium is liquid

B Magnesium melts at 650^oC - temperature is 730^oC so magnesium is liquid

C Magnesium has density 1.74 g cm^-3 and floats in magnesium chloride (2.32g cm^-3)

D Magnesium formed is a liquid at 730^oC and floats in molten magnesium chloride as magnesium metal has a lower density.

Which of the following compounds is a base?

• Sodium carbonate

• Sodium chloride

• Sodium nitrate

• Sodium sulfate

Answer explanation

A base is a chemical which neutralises an acid to form water

e.g. metal hydroxides (alkalis), metal oxides and metal carbonates are bases

AgNO₃(aq) + KCl(aq) --> AgCl(s) + KNO₃(aq)

Which of the following are the spectator ions in this reaction?

• Ag⁺ and Cl⁻

• K⁺ and NO₃⁻

• Ag⁺ and NO₃⁻

• K⁺ and Cl⁻

Answer explanation

x H₂O₂ --> y H₂O + z O₂

This equation will be balanced when

• x = 1, y = 2 and z = 2

• x = 1, y = 1 and z = 2

• x = 2, y = 2 and z = 1

• x = 2, y = 2 and z = 2

Answer explanation

2H₂O₂ --> 2H₂O + O₂

0·25 moles of a gas has a mass of 7 g.

Which of the following could be the molecular formula for the gas?

• C₂H₆

• C₂H₄

• C₃H₈

• C₃H₆

Which of the following solutions contains the least number of moles of solute?

• 100 cm³ of 0·4 mol l⁻¹ solution

• 200 cm³ of 0·3 mol l⁻¹ solution

• 300 cm³ of 1·0 mol l⁻¹ solution

• 400 cm³ of 0·5 mol l⁻¹ solution

Answer explanation

A no of mol = volume x concentration = 0.1 litres x 0.4mol l-1 = 0.04mol

B no of mol = volume x concentration = 0.2 litres x 0.3mol l-1 = 0.06mol

C no of mol = volume x concentration = 0.3 litres x 1.0mol l-1 = 0.3mol

D no of mol = volume x concentration = 0.4 litres x 0.5mol l-1 = 0.2mol

Which of the following could be the molecular formula for an alkane?

• C₇H₁₆

• C₇H₁₄

• C₇H₁₂

• C₇H₁₀

Answer explanation

A C₇H₁₆ gives a general formula of C_nH_2n+2. Alkanes have general formula C_nH_2n+2.

B C₇H₁₄ gives a general formula of C_nH_2n. Alkanes have general formula C_nH_2n+2.

C C₇H₁₂ gives a general formula of C_nH_2n-2. Alkanes have general formula C_nH_2n+2.

D C₇H₁₀ gives a general formula of C_nH_2n-4. Alkanes have general formula C_nH_2n+2.