Calculate the grams or milliliters of solute needed to prepare the following solutions.
(PART A) 60. gg of a 3.0 % (m/m) KCl solutionExpress your answer using two significant figures. (Answer should be in grams
The Correct Answer and Explanation is:
To solve this problem, we will use the formula for mass/mass percent concentration (% m/m):
$$
\text{mass percent} = \left( \frac{\text{mass of solute}}{\text{mass of solution}} \right) \times 100
$$
Given:
- Mass percent (% m/m) = 3.0%
- Mass of solution = 60. g (note: “gg” seems to be a typo)
- Unknown: mass of solute (in grams)
Step 1: Rearranging the formula
To find the mass of solute, rearrange the formula:
$$
\text{mass of solute} = \left( \frac{\text{mass percent}}{100} \right) \times \text{mass of solution}
$$
Step 2: Plug in the values
$$
\text{mass of solute} = \left( \frac{3.0}{100} \right) \times 60
$$
$$
\text{mass of solute} = 0.03 \times 60 = 1.8 \, \text{g}
$$
✅ Final Answer: 1.8 g
✏️ Explanation (300 words)
This problem involves preparing a potassium chloride (KCl) solution where the concentration is given in terms of mass/mass percent (% m/m). The mass/mass percent tells us how many grams of solute are present in 100 grams of the entire solution. A 3.0% (m/m) solution means that there are 3 grams of KCl in every 100 grams of solution.
In this case, we are told we need 60 grams of the entire solution, and we are asked to find how many grams of KCl (solute) are needed to make this.
To find that, we use the equation:
$$
\text{mass of solute} = \left( \frac{\text{percent concentration}}{100} \right) \times \text{mass of solution}
$$
This formula works by taking the proportion of the solution that is KCl (3.0%, or 0.03 when expressed as a decimal), and multiplying it by the total solution mass (60 g). This gives:
$$
0.03 \times 60 = 1.8 \, \text{g of KCl}
$$
This value represents the amount of potassium chloride you must weigh and dissolve in enough water to reach a total solution mass of 60 grams. It’s important not to add 60 grams of water, but rather to add enough water to bring the total mass (solute + solvent) up to 60 grams.
This concept is frequently applied in laboratory and clinical settings, where accurate concentrations are needed for chemical reactions, medication dosing, or IV fluid preparations.
