Chemistry Moles

Question 1

How many atoms are there in one mole of O atom

Answer 1

6.02 ✖10^23 atoms

Question 2

From the solution in each tube , the student obtained crystals with the formula MgCl2⃣.6H2⃣O
Calculate the relative formula
Mg=24.3
Cl = 35.5
H = 1
O = 16

Answer 2

203.3 g mol ^-1

Question 3

Calculate the number if moles in a solid

Answer 3

Moles = mass of substance ➗ molar mass

Question 4

A Bronze Age shield found on Dartmoor contained 2.08 kg of tin.
Calculate the number of tin atoms in the shield.

Answer 4

2.08 ✖1000 = 2080

2080 ➗ 118.7 = 17.5 mol

Question 5

Calculating number of moles in a liquid

Answer 5

Moles = (concentration ✖ volume) ➗ 1000

Question 6

What volume of 0.1 M of sulphuric acid contains 0.002 moles?

Answer 6

(1000 ✖ 0.002) ➗ 0.1 = 20 cm^3

Question 7

Calculating moles when given a gas

Answer 7

Moles = volume ➗ 24(000)

Question 8

Analysis of a compound shows that it contained 74.19% of Na and 25.81% of O. What is the empirical formula of this compound?

Answer 8

Na

74. 19 ➗ 23 = 3.23
75. 23 ➗ 1.61 = 2

O

25. 81 ➗ 16 = 1.61
26. 61 ➗ 1.61 = 1

Na2⃣O

Question 9

Calculate the molecular formula of a compound of empirical formula CH2⃣ and relative molecular mass of 84

Answer 9

Mass of CH2⃣ = 14
84 ➗ 14 = 6
C6⃣H1⃣2⃣

Question 10

Sodium ➕ water ——> sodium hydroxide ➕ hydrogen

Balance symbol equation with state symbols

Answer 10

2Na (s) ➕ 2H2⃣O (l) —–> 2NaOH (aq) ➕ H2⃣ (g)

Question 11

Calculate the volume of 0.1 M of hydrochloric acid which neutralise 23.55 cm^3 of 0.12 M of sodium hydroxide

Answer 11

HCl ➕ NaOH —–> NaCl ➕ H2⃣O
n of NaOH = 0.12 ➗ 23.5 = 0.002826 mol
N of HCl = 0.002826 mol
V = (0.002826 ✖ 1000) ➗ 0.1 = 28.26 cm^3

Question 12

Sodium nitrate decomposes on heating as follows
2NaNO3⃣ —–> 2NaNO2⃣ ➕ O2⃣
What volume of oxygen is produced when 6.8 g sodium nitrate is heated?

Answer 12

n of NaNO3⃣= 6.8 ➗ 69 = 0.09855 mol
n of O2⃣ = 0.09855 ➗ 2 = 0.04928 mol
V of O2⃣ = 0.04928 ✖ 24 = 1.18 dm^3