Chemistry, 04.08.2019 00:30 izearaholland7308

Calculate the freezing point of a solution containing 5.7 % kcl by mass (in water).

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Answer from: Madi2277

5.7% KCl is 94.3 % water.
Therefore, for 1000 g of water the mass of KCl will be (1000× 5.7)/94.3 = 60.445 grams.
1 mole of KCl is equal to 74.55 g,
therefore, 60.445 g will be 60.445/74.55 = 0.8108 mole of KCl
Hence, 0.8108 moles of KCl should release twice that number of moles 1.6216 moles ions.
Having 1.6216 moles of KCl ions dissolved in 1000g of water, gives us 1.6216 molar if solution.
Using the freezing point depression constant of water.
dT = Kf (molarity)
dT = (1.86 C/ molar) (1.6216 m)
dT = 3.016 C drop in freezing point
Therefore, it should freeze at - 3.016 Celsius

Answer from: skwmks8924

Mass percent of KCl = 5.7%
So the Mass percent of water = 100 - 5.7 = 94.3%
KCl mixed in 1000 grams of water = (5.7 / 94.3) x 1000 = 60.44 grams Calculating the moles of KCl = mass of KCL / molecular weight
= 60.44 / (K (39.1) + Cl(35.5)) = 60.44 / 74.6 = 0.81 moles and KCl release twice the moles, so 2 x 0.81 = 1.62 moles
So the molarity M = 1.62,
Kf is the freezing point depression constant of the solvent, here water
So Kf = 1.86 °C/m
Freezing point temperature dT = Kf x M = 1.86 x 1.62 = 3.01 C

Answer from: Quest

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.

chemical decomposition is opposite of chemical synthesis.

Answer from: Quest

the link still does not work even when adding it to the url bar

explanation:

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Calculate the freezing point of a solution containing 5.7 % kcl by mass (in water)....