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3 years ago

which best describes an element? - a pure substance - a type of a mixture - a pure compound - an impure substance

Chemistry

2 answers:

Nikitich [7]3 years ago

7 0

An element is a pure substance which means it cannot be broken down by any means.

STatiana [176]3 years ago

4 0

Answer:

A pure substance

Explanation:

An element is a pure substance.

It is only made up of atoms of the same type.

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in order to find the molar mass of an unknown compound, a research scientist prepared a solution of 0.930 g of an unknown in 125

PtichkaEL [24]

Answer:

Molar mass→ 0.930 g / 6.45×10⁻³ mol = 144.15 g/mol

Explanation:

Let's apply the formula for freezing point depression:

ΔT = Kf . m

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ΔT = Kf . m → ΔT / Kf = m

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3 years ago

Answer the following questions based on the reaction below: NaOH(aq) + KHP(s) --> NaKP(aq)+H2O(I)

Natali [406]

Answer:

a) 1.44g

b) 77.3%

Explanation:

1. Chemical balanced equation (given)

$NaOH(aq)+ KHP(s)\rightarrow NaKP(aq)+H_2O(l)$

2. Mole ratio

$1molNaOH(aq):1molKHP(s)$

This is, 1 mol of NaOH will reacts with 1 mol of KHP.

3. Find the number of moles in 72.14 mL of the base

$Molarity=\text{number of moles of solute}/\text{volume of solution in liters}$

$\text{Volume of solution}=72.14mL=0.07214liters$

$\text{Number of moles of NaOH}=0.0978M\times 0.07214liter=0.007055mol$

4. Find the number of grams of KHP that reacted

The number of moles of KHP that reacted is equal to the number of moles of NaOH, 0.007055 mol

Convert moles to grams:

mass = number moles × molar mass = 0.007055mol × 204.23g/mol

mass = 1.4408 g.

You have to round to 3 significant figures: 1.44 g (because the molarity is given with 3 significant figures).

5. Find the percentage of KHP in the sample

The percentage is how much of the substance is in 100 parts of the sample.

The formula is:

% = (mass of substance / mass of sample) × 100

% = (1.4408g/ 1.864g) × 100 = 77.3%

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