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3 years ago

1. Which of the following statements about mechanical waves is true?

Chemistry

1 answer:

Anna [14]3 years ago

6 0

1. The answer is "a".

Mechanical waves require a medium to travel. If there is no medium, the mechanical wave doesn't travel. Since, they are waves; they have a wavelength, frequency, speed and also amplitude. The speed depends on the medium and type of the wave. An example for the mechanical waves is sound wave.

2. E = hf, where E is energy, h is plank constant and f is the frequency. Hence, if the frequency is high, then the energy is high.

v = fλ , where v is the speed, f is the frequency and λ is the wavelength. If the frequency is high, then the wavelength is low.

According to the given choices, gamma rays have the shortest wavelength and highest energy on electromagnetic spectrum.

3. The wavelength of X-rays are smaller the wavelength of infrared.

According to the v=fλ, lower the wavelength, then higher the frequency. According to the E = hf, if the frequency is high, then the energy is also high.

Hence, the correct answer is "d"

4. In a longitudinal wave (compression wave) the particles of a matter move parallel.

There are two types of waves according to the particle movement. They are transverse waves and longitudinal waves. In transverse waves, the particles of the medium move perpendicular to the direction of the wave and longitudinal waves have parallel movement of particles to the direction of wave.

5. In regard to spend of sound, sound travels slowest in gases.

Solids have the highest speed of sound while gases have the lowest. This is because of the particle arrangement of each phase. Solid phase has very tightly packed particle arrangement and due to that the transfer of sound wave in easy than in gases.

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A chemist must prepare of sodium hydroxide solution with a pH of at . He will do this in three steps: Fill a volumetric flask ab

77julia77 [94]

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0.0400 g for the example given below.

Explanation:

pH value is not provided, so we'll solve this problem in a general case and then we will use an example to justify it.

By definition, $pH = -log[H_3O^+]$ .
NaOH is a strong base, as it's a hydroxide formed with a group 1A metal, so it dissociates fully in water by the equation: $NaOH (aq)\rightarrow Na^+ (aq) + OH^- (aq)$ .
From the equation above, using stoichiometry we can tell that the molarity of hydroxide is equal to the molarity of NaOH: $[NaOH] = [OH^-]$ .
Concentration of hydroxide is then equal to the ratio of moles of NaOH and the volume of the given solution. Moles themselves are equal to mass over molar mass, so we obtain: $[OH^-] = [NaOH] = \frac{n_{NaOH}}{V} = \frac{m_{NaOH}}{M_{NaOH}V}$ .
We also know that $pOH = 14.00 - pH = -log[NaOH]$ . Take the antilog of both sides: $10^{-pOH} = 10^{pH - 14.00} = [NaOH] = \frac{m_{NaOH}}{M_{NaOH}V}$ .
Solve for the mass of NaOH: $m_{NaOH} = 10^{pH - 14.00}\cdot M_{NaOH}\cdot V$ .

Now, let's say that pH is given as 12.00 and we use a 100-ml volumetric flask. Then we would obtain:

$m_{NaOH} = 10^{12.00 - 14.00}\cdot 39.997 g/mol\cdot 0.100 L = 0.0400 g$

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2 years ago

(23.4m)(14m) rounded off to the correct number of significant figures

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The value of the given expression up to correct significant figures is $330 m^2$ .

The rule that applies for the multiplication and division is :

The least number of significant figures in any number of the problem determines the number of significant figures in the answer.