Chemistry Jamb Question and Answers

Chemistry  Jamb Past And Answers That Fall Under The Topic 'Atoms, Moles, Formulae And Equations''

Questions No 18,,

What is the concentration of a solution containing 2g of NaOH in 

100cm3 of solution? 

A. 0.40 mol dm-3

B. 0.50 mol dm-3

C. 0.05 mol dm-3

D. 0.30 mol dm-3

[Na = 23, O =16, H =1] 

Solution 

You Must Convert The Volume From Cm3 to dm3. 100cm3/1000 = 0.1 dm3

First calculate the molar mass of NaOH which,

23+16+1=40g/mol

Then number of moles of NaOH = mass in gram/molar mass

Moles of NaOH = 2/40 = 0.05 moles 

Then concentration =number of moles/ volume in dm³

Conc. = 0.05/0.1=0.5 mol/dm3.

Option C 👍 is the answer 

Questions No 19,

How many atoms are present in 6.0g, of magnesium? 

A. 1.20 x 1022

B. 2.41 x 1022

C. 1.51 x 1023

D. 3.02 x 1023

[Mg =24, NA =6.02 x 1023 mol-1]

Solution

First calculate the number of moles in 6.0g of mg

Moles=mass in gram/molar mass= 6/24 = 0.25 mole. 

In each mole there are 6.02x 10²³ atoms

So number of atoms in 0.25 mole of my is 

N. Atoms = N. Mole x avogdros number 

N. Atoms = 0.25 x 6.02 x10²³ = atoms 

N. Atoms = 1.51 x 10²³ atoms

C✅