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Svetach [21]
3 years ago
8

Calculate the moles of solute dissolved in 4.2 dm3 of a 0.5 mol / dm3 solution.

Chemistry
1 answer:
Archy [21]3 years ago
8 0

Answer:

Example

0.5 mol of sodium hydroxide is dissolved in 2 dm3 of water. Calculate the concentration of the sodium hydroxide solution formed.

Concentration =

Concentration = 0.25 mol/dm3

Volume units

Volumes used in concentration calculations must be in dm3, not in cm3. It is useful to know that 1 dm3 = 1000 cm3. This means:

divide by 1000 to convert from cm3 to dm3

multiply by 1000 to convert from dm3 to cm3

For example, 250 cm3 is 0.25 dm3 (250 ÷ 1000). It is often easiest to convert from cm3 to dm3 before continuing with a concentration calculation.

Question

100 cm3 of dilute hydrochloric acid contains 0.02 mol of dissolved hydrogen chloride. Calculate the concentration of the acid in mol/dm3.

Reveal answer

Converting between units

The relative formula mass of the solute is used to convert between mol/dm3 and g/dm3:

to convert from mol/dm3 to g/dm3, multiply by the relative formula mass

to convert from g/dm3 to mol/dm3, divide by the relative formula mass

Remember: the molar mass is the Ar or Mr in grams per mol.

Example

Calculate the concentration of 0.1 mol/dm3 sodium hydroxide solution in g/dm3. (Mr of NaOH = 40)

Concentration = 0.1 × 40

= 4 g/dm3

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Describe the relationship between frequency and wavelength in your own words
Montano1993 [528]
Are frequency and wavelength the same thing? No, they are not the same but each is mathematically related to the other. Effectively, the wavelength is the distance between one wave peak and the next wave peak, or in other words, the distance between one wave high point and the next high point. Alternatively it could of course be said that wavelength is the distance between one wave low point and the next wave low point, but lets not get pedantic about it.

Think of waves in the ocean where a person may be observing the top of one wave and the top of the next wave. The wavelength is the distance between these two wave tops, or peaks. With waves in the ocean, the frequency of the waves will be the number of times that a wave peak crosses any given point on the ocean. It is probably easiest to measure frequency of waves from the ocean by standing on the beach and counting how many waves come up on the sand relative to any given time frame. Frequency is typically measured in how many waves per second but with ocean waves we are better to measure how many waves per minute because naturally the frequency will be less than one per second.

There is actually quite a bit of science over how ocean waves travel around our planet because high and low tide in the ocean are created by the moon. There is a theory that the moon creates waves that have a wavelength equal to half of the circumference of planet Earth. This is because there is a high tide at Earths point that is closest to the moon and then another high point that is at the greatest distance from the moon. The problem is that to keep up with the moon one needs to travel around the Earths equator at about 1800 kph, which is impractical for an ocean wave because they quite simply cannot travel at that fast a speed or velocity (technically angular velocity). This is what causes ocean waves to become so messy at times.

When discussing waves, most people are most comfortable discussing electromagnetic waves because almost all communication systems relied on in modern society are based on these waves and their frequency. When collecting electromagnetic waves, like TV waves, for example, there are several components to the antenna. One of them will typically have a loop of metal, which is where the required energy waves (carrying the required signal) are picked up or collected by the antenna. Don’t worry about the other components of the antenna because most are there simply to remove unwanted background waves that may spoil the quality of the signal that we collect. With the TV antenna, the distance across this “collection loop” is the wavelength that the antenna is tuned to collect.

The reason for a loop on the piece of metal that collects TV waves, rather than using a straight piece of wire, is so that all wavelengths that are close to the required one, will be collected. To get slightly more technical, in modern systems we have “frequency modulation”, which is what FM stand for. This means we deliberately make minor adjustments to the precise frequency, but I better not go into that.

The frequency of a TV wave that is being collected is the number of times in any time frame, that a wave front or wave peak, will cross the collection point. With typical electromagnetic waves like TV waves, we use a frequency that is measured to be so many Hertz. The Hertz is the standard measure of such things and it is equal to a number of wavelengths per second. The reason for this is that electromagnetic waves travel at the speed of light, which is incredibly fast.

If we are talking in the old fashioned “long wave” AM radio waves, then the wavelength is often several hundred metres in length. In Melbourne, Australia, the nearest large city to my home, the government owned ABC used a frequency of 774 kHz for many decades. They still do in fact, although most people tuned in probably rely on a repeater station these days and these will broadcast in a higher frequency. 774 kHz is a frequency of 774 thousand cycles per second. This sounds like a high frequency when compared to most other waves, even sound waves, yet because radio waves travel so fast, the wavelength is slightly greater than 387 metres in wavelength, which is almost 424 yards in wavelength.

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6.3K viewsView 3 Upvoters
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6 0
3 years ago
What are examples of chemical change
VladimirAG [237]

Answer:

Almost everything in our surroundings represent chemical change

Explanation:

●Rusting of iron in presence of moisture and oxygen.

●Burning of wood.

●Milk becoming curd.

●Formation of caramel from sugar by heating.

●Baking of cookies and cakes.

●Cooking any food.

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3 0
2 years ago
Hydrogen produced from a hydrolysis reaction was collected over water and the following data was compiled.
Shkiper50 [21]

Answer:

  • 0.00358 mol

Explanation:

<u>1) Data:</u>

a) V = 93.90 ml

b) T = 28°C

c) P₁ = 744 mmHg

d) P₂ = 28.25 mmHg

d) n = ?

<u>2) Conversion of units</u>

a) V = 93.90 ml × 1.000 liter / 1,000 ml = 0.09390 liter

b) T = 28°C = 28 + 273.15 K = 301.15 K

c) P₁ = 744 mmHg × 1 atm / 760 mmHg = 0.9789 atm

d) P₂ = 28.5 mmHg × 1 atm / 760 mmHg = 0.0375 atm

<u>3) Chemical principles and formulae</u>

a) The total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas. Hence, the partical pressure of the hydrogen gas collected is equal to the total pressure less the vapor pressure of water.

b) Ideal gas equation: pV = nRT

<u>4) Solution:</u>

a) Partial pressure of hydrogen gas: 0.9789 atm - 0.0375 atm = 0.9414 atm

b) Moles of hygrogen gas:

pV = nRT ⇒ n = pV / (RT) =

n =  (0.9414 atm × 0.09390 liter) / (0.0821 atm-liter /K-mol × 301.15K) =

n = 0.00358 mol (which is rounded to 3 significant figures) ← answer

7 0
3 years ago
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