Chemical Calculations

Calculate the Mr of Na₂SO₄.10H₂O

• 142

• 178

• 322

• 161

Calculate the number of moles in 25.25g of KNO₃

• 2

• 0.25

• 0.75

• 4

Calculate the mass of 0.5 mol of NaOH

• 15g

• 10g

• 20g

• 40g

Scheelite is an ore of tungsten.

The main compound in scheelite has the percentage composition by mass

Ca = 13.9%, W = 63.9%, O = 22.2%.

Calculate the empirical formula of this compound. [Ca=40,W=184,O=16]

• CaWO

• CaWO₃

• CaWO₄

• Ca₂W₂O₃

Calculate the empirical formula of the compound with the following composition by mass:

26.6% K, 35.4% Cr, 38.0% O

[K=39, Cr=52, O=16]

• K₂Cr₂O₇

• KCrO₄

• K₂CrO₄

• KCrO₃

Find the empirical formula of the compound formed in the reaction of 10.800g of magnesium to form 18.000g of an oxide. [Mg=24, O=16]

• MgO

• MgO₂

• Mg₂O

• Mg₂O₂

A compound of carbon, hydrogen and nitrogen only has the following composition: C 77.4%, H 7.5%, N 15.1%. What is the empirical formula of the compound? [C=12,H=1,N=14]

• C₆H₈N

• C₆H₆N

• C₆H₇N

• CHN

A compound has the empirical formula CH₂O, and an Mr of 180. What is its molecular formula?

• CH₂O

• 6CH₂O

• 6(CH₂O)

• C₆H₁₂O₆

A hydrated salt of BaCl₂ has the formula BaCl₂.xH₂O. An experiment to determine x found 85.25% BaCl₂, 14.75% H₂O. Determine the value of x. [Ba = 137, Cl = 35.5, H=1,O=16]

• 3

• 5

• 2

• 8

Calculate the empirical formulae of the following compounds from the information given: 5.8 g of aluminium combines with 22.9 g of chlorine. [Al = 27, Cl = 35.5]

• AlCl

• AlCl₂

• AlCl₃

• AlCl₄