What mass of sodium bromide (NaBr) is required to make 250 cm3 of a 0.35 mol.dm-3 solution?
How many mol NaBr do you need? That is M x dm^3 = ?
Then mol NaBr = grams NaBr/dm^3
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To find the mass of sodium bromide (NaBr) required to make a solution, you need to use the formula:
Mass = Volume x Concentration x Molar Mass
In this case, you have the volume (250 cm3) and concentration (0.35 mol.dm-3). However, you still need to find the molar mass of NaBr.
The molar mass of NaBr can be calculated by adding the atomic masses of sodium (Na) and bromine (Br). The atomic mass of sodium is 22.99 g/mol, and bromine is 79.90 g/mol.
So, the molar mass of NaBr is 22.99 g/mol + 79.90 g/mol = 102.89 g/mol.
Now, you can calculate the mass of NaBr:
Mass = Volume x Concentration x Molar Mass
Mass = 250 cm3 x 0.35 mol.dm-3 x (102.89 g/mol / 1000 cm3/dm3)
First, convert cm3 to dm3:
250 cm3 = 250/1000 dm3 = 0.25 dm3
Now, substitute the values into the formula:
Mass = 0.25 dm3 x 0.35 mol.dm-3 x (102.89 g/mol / 1000 cm3/dm3)
Mass = 0.25 dm3 x 0.35 mol.dm-3 x 0.10289 g/cm3
Multiply the numbers together:
Mass = 0.00896 g
Therefore, you will need approximately 0.00896 grams of sodium bromide (NaBr) to make 250 cm3 of a 0.35 mol.dm-3 solution.