Question

How many grams of solute are needed to prepare 5L of a $ 0.250{{M}} $ solution of $ Ca{\left( {N{O_3}} \right)_2} $ ?

Answer 1

Hint: We are already provided with the element. From the formula of molarity, we shall find the moles of solute required and thus, the weight of the solute.

Formula used: $ {{molarity = }}\dfrac{{{\text{ moles of solute }}}}{{{\text{volume of solution}}}} $

Complete step by step answer
We already know that prepare 5L of a $ 0.250{{M}} $ solution of $ Ca{\left( {N{O_3}} \right)_2} $
If the sample was measured in grams, we would first need to convert it to moles and then determine the amount of solute.
Because we already have the sample in a molar quantity, the moles of solute can be found out by:
 $ {{molarity = }}\dfrac{{{\text{ moles of solute }}}}{{{\text{volume of solution}}}} $
So, we have $ 0.250 $ moles of solute. Converting this to mass from the gram molecular weight, we obtain:
 $ {{moles = 0}}{{.250 \times 5 = 2}}{{.50mol}} $
 $ {\text{mass of solute} = moles \times \text{molar mass}} $
By putting the values in the formula:
 $ 2.50{{mol}} \times 164.09{{g}}{{.mo}}{{{l}}^{{{ - 1}}}} = 400{{g}} $
So, the weight of solute is 400g.

Additional Information
We should know that in order to calculate If two water samples have different volumes, they still share a common measurement: the density. Density is another measurement derived from SI basic units. The density of a material is defined as its mass per unit volume. We should know that in order to calculate the number of moles of any substance present in the sample, we simply divide the given weight of the substance by its molar mass. Where 'n' is the number of moles, 'm' is the given mass and 'M' is the molar mass. A mole is defined as the mass of the substance which consists of the equal quantity of basic units. Example atoms in 12 grams are the same as 12C. The basic units can be molecules, atoms or formula units based on the substance.
One mole of any substance is equal to the value of $ 6.023 \times {10^{23}} $ (Avagadro number). It can be used to measure the products obtained from the chemical reaction. The unit is denoted by mol.

Note
We already know that the molecular formula to find the molar mass; to obtain the number of moles, divide the mass of the compound by the molar mass of the compound expressed in grams.
All the values should be put carefully and the equations should be solved neatly.