Photo AI

In order to help prevent tooth decay, fluoride ions at a level of 0.9 mg L^{-1} of F^{-} are added to Melbourne’s public water supplies - VCE - SSCE Chemistry - Question 4 - 2004 - Paper 1

Question 4

$In-order-to-help-prevent-tooth-decay,-fluoride-ions-at-a-level-of-0.9-mg-L^{-1}-of-F^{-}-are-added-to-Melbourne’s-public-water-supplies-VCE-SSCE Chemistry-Question 4-2004-Paper 1.png$

In order to help prevent tooth decay, fluoride ions at a level of 0.9 mg L^{-1} of F^{-} are added to Melbourne’s public water supplies. The fluoride ions are obtain... show full transcript

Worked Solution & Example Answer:In order to help prevent tooth decay, fluoride ions at a level of 0.9 mg L^{-1} of F^{-} are added to Melbourne’s public water supplies - VCE - SSCE Chemistry - Question 4 - 2004 - Paper 1

Step 1

Calculate the mass of sodium fluoride in mg that must be present in one litre of water to produce a concentration of fluoride ions of 0.90 mg L^{-1}.

96%

114 rated

Answer

To find the mass of sodium fluoride (NaF) required to achieve a fluoride ion concentration of 0.90 mg L^{-1}, we can use the molar mass of NaF.

The molar mass of NaF is approximately 42.0 g/mol.

Since 0.9 mg of fluoride ions corresponds to:

$ext{Mass of F}^{-} = 0.90 ext{ mg} = 0.90 imes 10^{-3} ext{ g}$
Next, calculate the moles of fluoride ions:

$n = rac{ ext{mass}}{ ext{molar mass}} = rac{0.90 imes 10^{-3}}{19.0} ext{ mol}$
Then, calculate the total mass of sodium fluoride required:

$ext{mass of NaF} = n imes ext{molar mass of NaF} = rac{0.90 imes 10^{-3}}{19.0} imes 42.0 ext{ g} = 2.0 ext{ mg}$

Thus, the mass of sodium fluoride needed in one litre is 2.0 mg.

Step 2

What mass of sodium fluoride, in kilogram, must be added to a 750 ML reservoir (1 ML = 10^{-6} L) to produce a concentration of fluoride ions of 0.90 mg L^{-1}?

99%

104 rated

Answer

To calculate the mass of sodium fluoride for a 750 mL reservoir, follow these steps:

First, convert 750 mL to litres:

$750 ext{ mL} = 750 imes 10^{-3} ext{ L} = 0.750 ext{ L}$
Calculate the total amount of fluoride ions needed for 0.750 L:

$ext{mass of F}^{-} = ext{concentration} imes ext{volume} = 0.90 ext{ mg L}^{-1} imes 0.750 ext{ L} = 0.675 ext{ mg}$
Next, convert mg to kg:

$0.675 ext{ mg} = 0.675 imes 10^{-3} ext{ g} = 1.5 imes 10^{-6} ext{ kg}$
Calculate the mass of NaF:

$ext{mass of NaF} = rac{0.675 imes 10^{-3} ext{ g}}{19.0} imes 42.0$

The total mass needed is approximately 1.5 x 10^{-3} kg.

Step 3

Calculate the number of fluoride ions swallowed by a person who drank one litre of water from the reservoir.

96%

101 rated

Answer

To find the number of fluoride ions in 1 litre of water:

Calculate the mass of fluoride in 1 L using the previous concentration:

$ext{mass of F}^{-} = 0.90 ext{ mg L}^{-1} imes 1 ext{ L} = 0.90 ext{ mg} = 0.90 imes 10^{-3} ext{ g}$
Determine moles of fluoride ions:

$n = rac{ ext{mass}}{ ext{molar mass}} = rac{0.90 imes 10^{-3}}{19.0} ext{ mol}$
Convert moles to number of ions:

Use Avogadro's number ( $N_A ext{ = } 6.022 imes 10^{23} ext{ mol}^{-1}$ ) to determine:

$ext{Number of ions} = n imes N_A$

This results in approximately 2.91 imes 10^{19} fluoride ions in one litre.

In order to help prevent tooth decay, fluoride ions at a level of 0.9 mg L^{-1} of F^{-} are added to Melbourne’s public water supplies - VCE - SSCE Chemistry - Question 4 - 2004 - Paper 1

Worked Solution & Example Answer:In order to help prevent tooth decay, fluoride ions at a level of 0.9 mg L^{-1} of F^{-} are added to Melbourne’s public water supplies - VCE - SSCE Chemistry - Question 4 - 2004 - Paper 1

Calculate the mass of sodium fluoride in mg that must be present in one litre of water to produce a concentration of fluoride ions of 0.90 mg L^{-1}.

What mass of sodium fluoride, in kilogram, must be added to a 750 ML reservoir (1 ML = 10^{-6} L) to produce a concentration of fluoride ions of 0.90 mg L^{-1}?

Calculate the number of fluoride ions swallowed by a person who drank one litre of water from the reservoir.

Join the SSCE students using SimpleStudy...