Answer:
0.91 g NaF
Explanation:
Mass percentage is one way of representing the concentration of an element in a compound or a component in a mixture. Mass percentage is calculated as the mass of a component divided by the total mass of the mixture, multiplied by 100%.
Let mass of NaF = x g
∴ mass percent = mass of NaF / mass of total mixture *100
3.5 = (x/ x + 25) * 100
∴ x = 0.91 g
Answer: The mass of NaF that must be mixed with 25 mL of water is 0.91 grams
Explanation:
We are given:
Volume of water = 25 mL
To calculate the mass of water, we use equation used to calculate density:
[tex]\text{Density of substance}=\frac{\text{Mass of substance}}{\text{Volume of substance}}[/tex]
Density of water = 1 g/mL
Volume of water = 25 mL
Putting values in above equation, we get:
[tex]1g/mL=\frac{\text{Mass of water}}{25mL}\\\\\text{Mass of water}=(1g/mL\times 25mL)=25g[/tex]
We are given:
3.5 % (m/m) NaF solution
This means that 3.5 grams of NaF is present in 100 g of solution
Mass of water in solution = 100 - 3.5 = 96.5 g
To calculate the mass of NaF mixed with 25 mL of water, we use unitary method:
In 96.5 grams of water, the mass of NaF added is 3.5 grams
So, in 25 grams of water, the mass of NaF that must be added will be = [tex]\frac{3.5}{96.5}\times 25=0.91g[/tex]
Hence, the mass of NaF that must be mixed with 25 mL of water is 0.91 grams
