Question

1. Calculate the number of moles of [2]
(a)chloride ions in 79.17 g of magnesium chloride, MgCl2

Answer 1

Answer:

Step 1: Write out the chemical formula of the compound.

Magnesium Chloride =

M

g

C

l

2

Step 2: Convert moles into number of compounds using Avogadro's number

0.5 moles

M

g

C

l

2

⋅

(

6.022

⋅

10

23

1 mole

M

g

C

l

2

)

=

3.011

⋅

10

23

Step 3: Determine how many Chloride ions there will be in 1 compound

There will be 2

C

l

−

ions in each compound (

C

l

2

part)

Step 4: Multiply the number from Step 2 by the number in Step 3

3.011

⋅

10

23

⋅

2

=

6.022

⋅

10

23

We do this because the ratio is 2

C

l

−

ions for every 1 compound.

In the case of finding how many ions in general (both sodium and chloride), we would multiply by 3 because there are 3 ions per 1 compound.

Step 5: All done!

I hope this helped

Answer 2

Answer:

There are 0.0016 mol chloride ions in this sample of magnesium chloride.

Magnesium chloride has the chemical formula

M

g

C

l

2

. From this equation, we can determine the molar mass of magnesium chloride.

24.305

g

/

m

o

l

+

(

2

)

(

35.45

g

/

m

o

l

)

=

95.205

g

/

m

o

l

Now we can determine the moles of chloride ions in 0.0750 g of magnesium chloride.

0.0750

g

M

g

C

l

2

×

1

m

o

l

M

g

C

l

2

92.205

g

M

g

C

l

2

×

2

m

o

l

C

l

−

1

m

o

l

M

g

C

l

2

=

0.0016

m

o

l

C

l

−