The GRESA method stands for:

• G (Given) – Identify given values.
• R (Required) – Determine what needs to be found.
• E (Equation) – Write the formula to use.
• S (Solution) – Solve using the equation.
• A (Answer) – State the final answer with units.

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Problem 1: Molarity of CaO Solution

Step 1: Given (G)

• Mass of CaO = 10.5 g
• Volume of solution = 2,500 mL = 2.5 L
• Molar mass of CaO = 40.08 + 16.00 = 56.08 g/mol

Step 2: Required (R)

• Find Molarity (M) = moles of solute / liters of solution

Step 3: Equation (E)

$M = \frac{\text{moles of solute}}{\text{liters of solution}}$ $\text{moles of CaO} = \frac{\text{mass}}{\text{molar mass}}$

Step 4: Solution (S)

$\text{moles of CaO} = \frac{10.5 \text{ g}}{56.08 \text{ g/mol}} = 0.1873 \text{ moles}$

$M = \frac{0.1873}{2.5} = 0.0749 \text{ M}$

Step 5: Answer (A)

The molarity of the solution is 0.0749 M.

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Problem 2: Dilution of NaCl Solution

Step 1: Given (G)

• Initial volume $V_1$ = 40 mL
• Initial molarity $M_1$ = 0.60 M
• Final volume $V_2$ = 130 mL

Step 2: Required (R)

• Find Final concentration $M_2$

Step 3: Equation (E)

$M_1 V_1 = M_2 V_2$

Step 4: Solution (S)

$(0.60 M)(40 \text{ mL}) = M_2 (130 \text{ mL})$

$24 = 130 M_2$

$M_2 = \frac{24}{130} = 0.1846 \text{ M}$

Step 5: Answer (A)

The concentration of the diluted solution is 0.185 M.

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Would you like more details or a breakdown of any step?

Related Questions:

1. What is the difference between molarity and molality?
2. How does temperature affect molarity in solutions?
3. If 500 mL of 1.2 M HCl is diluted to 1.5 L, what is the new concentration?
4. What happens to the number of moles of solute when diluting a solution?
5. How do you calculate the final volume needed to reach a desired molarity?

Tip:

Always convert volume to liters in molarity calculations to ensure correct units! 🚀