Question

Medical cold packs can use various chemicals in order to produce a cold compress to help reduce inflammation caused by injuries. Based on the accepted value in Question 1, how many grams of potassium chloride would have to be dissolved into 750 g of 20.0°C water to produce a 4.0°C solution? (Remember: specific heat of water is 4184 J/g·°C) 92 4.

Answer 1

We need 217.7 grams of KCl

Step-by-step explanation:

Medical cold packs can use various chemicals in order to produce a cold compress to help reduce inflammation caused by injuries. Based on the accepted value of 17.2 kJ/mol, how many grams of potassium chloride would have to be dissolved into 750 g of 20.0 degree Celsius water to produce a 4.0 degree Celsius solution?

Step 1: Data given

Mass of water = 750 grams

Temperature = 20.0 °C

Temperature of the solution = 4.0 °C

Specific heat of water 4.184 J/g°C

Step 2: Calculate the heat

Q = m* c * ΔT

⇒with Q = the heat transfer = TO BE DETERMINED

⇒with m = the mass of water = 750 grams

⇒with c = the specific heat of water = 4.184 J/g°C

⇒with ΔT = The change of temperature = 16 °C

Q = 750 * 4.184 * 16

Q = 50208 J = 50.2 kJ

Step 3: Calculate moles KCl

Moles KCl = 50.2 kJ / 17.2 kJ/mol

Moles KCl = 2.92 moles

Step 4: Calculate mass KCl

Mass KCl = moles KCl * molar mass KCl

Mass KCl = 2.92 moles * 74.55 g/mol

Mass KCl = 217.7 grams

We need 217.7 grams of KCl

Answer 2

Mass of KCL = 218 grams.

Step-by-step explanation:

Step 1: calculate the heat that must be absorbed(q).

Heat that must be absorbed(q) is calculated as follows:

q= m c (T2-T1).

q = 750g (4.18 J/gC)(20-4 C) = 5.016X10^4 J = 50.16 kJ

Step 2: we determine moles of KCL as follows:

Moles KCl = 50.16 kJ / 17.2 kJ/mol = 2.92 moles.

Step 3: calculate mass of KCL:

Mass of KCl = 2.92 mol X 74.55 g/mol = 218g.

Therefore, 218 grams of KCL would have to be dissolved into 750 g of 20.0°C H2O to produce the solution.