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inysia [295]
3 years ago
7

4. A compact disc has a diameter of 11.8 cm. What is the surface area of the disc in square centimeters? In square meters? [Area

of a circle = (π)(radius) 2 ]
Chemistry
1 answer:
d1i1m1o1n [39]3 years ago
8 0
<span>The surface area is 109.3 square centimeters or 0.01093 square meters. The area formula requires that we use the radius of the disc. We can find the radius by diving the diameter by 2, so radius = 11.8/2 or 5.9 cm. We can use 3.14 as an approximation for π. The surface area is 3.14 * (5.9*5.9). Since the diameter is given in cm, the surface area units are in square centimeters. To convert to meters, divide any measurement in centimeters by 100, but we need to convert to "square" meters, so we need to divide our square centimeters by 100 * 100, or by 10,000. Dividing 109.3 by 10,000 results in 0.01093 square "meters".</span>
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Hydrofluoric acid, hf, has a ka of 6.8 × 10−4. what are [h3o+], [f−], and [oh−] in 0.710 m hf?
STALIN [3.7K]

Answer:

[H₃O⁺] = [F⁻] = 2.2 x 10⁻² M. & [OH⁻] = 4.55 x 10⁻¹³.

Explanation:

  • For a weak acid like HF, the dissociation of HF will be:

<em>HF + H₂O ⇄ H₃O⁺ + F⁻.</em>

[H₃O⁺] = [F⁻].

<em>∵ [H₃O⁺] = √Ka.C,</em>

Ka = 6.8 x 10⁻⁴, C = 0.710 M.

∴ [H₃O⁺] = √Ka.C = √(6.8 x 10⁻⁴)(0.710) = 2.197 x 10⁻² M ≅ 2.2 x 10⁻² M.

<em>∴ [H₃O⁺] = [F⁻] = 2.2 x 10⁻² M.</em>

<em></em>

∵ [H₃O⁺][OH⁻] = 10⁻¹⁴.

<em>∴ [OH⁻] = 10⁻¹⁴/[H₃O⁺]</em> = 10⁻¹⁴/(2.2 x 10⁻²) = <em>4.55 x 10⁻¹³.</em>

6 0
3 years ago
When performing physical exercise, the heart rate, by what percentage can it be increased?
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Answer:

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Lauryl alcohol is a nonelectrolyte obtained from coconut oil and is used to make detergents. A solution of 6.80 g of lauryl alco
natka813 [3]

Answer:

The approximate molar mass of lauryl alcohol is 174.08 g/m

Explanation:

An excersise to apply the colligative property of Freezing-point depression.

This is the formula: ΔT = Kf . m

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ΔT = T° pure solvent - T° fusion solution

Kf for benzene: 5.12 °C/m

5.5°C - 4.5°C = 5.12 °C /m  . m

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This moles of lauryl alcohol, solute, are in 1 kg of benzene, solvent.

I have to find out in 0.2 kg.

1 kg sv ____ 0.195 moles solute

0.2 kg sv ____ (0.195 . 0.2)/1 = 0.039 moles solute

The mass for these moles is 6.80 g, so if I want to know the molar mass, I have to divide mass / moles

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What are the 6 branches of chemistry and what do they study?
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