9th grade chemical reactions, acids and bases

Question 1

Alkanes have the general formula CₙH₂ₙ₊₂. How many hydrogen atoms are in an alkane with 10 carbon atoms?

Answer 

Question 2

Sodium hydroxide solution is added to a solution and a green precipitate forms. Which metal ion is present?

• A. copper(II), Cu²⁺
• B. iron(II), Fe²⁺
• C. iron(III), Fe³⁺
• D. calcium, magnesium or aluminium ions

Question 3

Balance the equation. What number goes in the gap? __Mg + O₂ → 2MgO

Answer 

Question 4

Why is gold found as the pure metal in the ground?

• A. It is very unreactive
• B. It is magnetic
• C. It is a non-metal
• D. It is very reactive

Question 5

Why should the wire loop be cleaned in acid before each flame test?

• A. to remove traces of the last compound that could change the colour
• B. to add sodium
• C. to make the flame hotter
• D. to stop the wire melting

Question 6

Which equation is correctly balanced?

• A. C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
• B. C₃H₈ + 5O₂ → 4CO₂ + 4H₂O
• C. C₃H₈ + 5O₂ → 3CO₂ + 3H₂O
• D. 2C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

Question 7

How does fractional distillation separate crude oil?

• A. Hydrocarbons condense at different heights of a column depending on their boiling points
• B. Each fraction is filtered out
• C. A magnet pulls out each fraction
• D. The oil is frozen in layers

Question 8

Rates of reaction: which statement is NOT true?

• A. A catalyst is not used up in a reaction.
• B. Increasing surface area increases the rate.
• C. Lower temperatures make reactions faster.
• D. Food lasts longer in a fridge because reactions are slower at low temperature.

Question 9

A reaction produces 80 cm³ of gas in 40 seconds. What is the mean rate of reaction, in cm³/s?

Answer cm³/s

Question 10

Hydrogen peroxide decomposes with a catalyst and the gas relights a glowing splint. Which gas is it?

• A. hydrogen
• B. carbon dioxide
• C. chlorine
• D. oxygen

Question 11

Tests for gases: which statement is NOT true?

• A. Limewater is a solution of calcium hydroxide.
• B. Chlorine may turn damp blue litmus red before bleaching it.
• C. Hydrogen gives a squeaky pop with a lighted splint.
• D. Carbon dioxide relights a glowing splint.

Question 12

Zn + 2HCl → ZnCl₂ + H₂ How many Cl atoms are on the right side of this balanced equation?

Answer 

Question 13

Reactivity series (most reactive first): potassium, sodium, calcium, magnesium, aluminium (aluminum), zinc, iron, copper, silver, gold. If calcium is added to a solution of aluminium (aluminum) sulfate, will a displacement reaction happen?

• A. yes
• B. no

Question 14

A flame test gives a lilac flame. Which metal ion is present?

• A. sodium, Na⁺
• B. potassium, K⁺
• C. calcium, Ca²⁺
• D. copper, Cu²⁺

Question 15

Why does a more concentrated acid react faster?

• A. The particles are heavier
• B. There are more acid particles in the same volume, so collisions are more frequent
• C. It is hotter
• D. It has a lower pH so no collisions are needed