MOLE CONCEPT (DK014)

Which of the following contains the same number of atoms?

[ A_r of Ca = 40 , A_r of S = 32 ]

• 1 g calcium and 1 g sulphur

• 10 g calcium and 8 gram sulphur

• 8 g calcium and 4 g sulphur

• 8 g calcium and 10 g sulphur

If 0.05 g of potassium hydroxide (KOH) is dissolved in 250 mL of water, what is the concentration of solution in mol L^-1?

[ A_r of K: 39.1 , A_r of O: 16 , A_r of H: 1 ]

• 0.003565

• 0.00833

• 0.0301

• 0.03565

What is the number of moles of oxygen gas that produce 90.0 L of volume at s.t.p?

• 5.0255

• 9.0197

• 4.0179

• 3.0798

A solution contains 28% sulphuric acid by mass. This means that

• 1 litre of solution contains 28 g of sulphuric acid

• 1 litre of solution has a mass of 28 g

• 100 g of solution contains 28 % of sulphuric acid

• 100 g of solution contains 28 g of sulphuric acid

What is the molarity of 4.0 g of NaCl (Molar mass of NaCl = 58.45) in 3800 mL of solution?

• 1.052 M

• 0.018 M

• 0.001M

• 0.062 M

How many grams of chloride ions are there in 100 mL of 1.90 M aqueous solution of sodium chloride?

[ A_r of Na: 23 , A_r of Cl: 35.5 ]

• 13.5 g

• 1.35 g

• 6.75 g

• 0.67 g

How much water need to prepare 200 mL of 0.1 M NaCl from 2.0 M NaCl solution?

• 190 mL

• 10 mL

• 200 mL

• 50 mL

A compound consists of 72.2% magnesium(Mg) and 27.8% nitrogen(N) by mass. What is the empirical formula?

[ A_r of Mg: 24.3 , A_r of N: 14 ]

• Mg₃N₂ 

• Mg₄N₃

• MgN₂

• MgN

Convert 25 g of NaBr to molecules.

[ A_r of Na: 23 , A_r of Br: 79.9 ]

• 0.24 molecules

• 102.96 molecules

• 1.45x10²³ molecules

• 2.34 x 10²⁰molecules

What is the empirical formula for thr compound, C_xH_yO_z , if the ratio of C: H: O equal to 2: 2.5 : 1 ?

• C₃H₂O₂

• C₄H₅O₂

• C₂H₂O₁

• C₂H₅O₁