CHEMISTRY COLLEGE

I have a cup of hot coffee at 140 oC but I want to cool it to 110 oC. My cup holds about 0.3 kg of coffee. Fortunately, I have a bunch of aluminum cubes in the freezer that I can drop into my hot coffee to cool it down. If each aluminum cube has a mass of 1 g (not 1 kg!) and my freezer keeps its contents at a temperature of –10 oC, how many cubes do I have to drop into my coffee? The specific heat of water is around 4000 joules/kg/oC and aluminum is about 900 joules/kg/oC. (Pick the answer closest to the true value and ignore any thermal losses to surroundings.)

A. 200
B. 330
C. 400
D. 110
E. 88

Answers

Answer 1

Answer:

Answer:

The correct answer is option B.

Explanation:

In this problem we assumed that heat given by the hot body is equal to the heat taken by the cold body.

$q_1=-q_2$

$m_1* c_1* (T_f-T_1)=-m_2* c_2* (T_f-T_2)$

where,

$C_1$ = specific heat of metal = $900 J/kg^oC$

$C_2$ = specific heat of coffee= $4000 J/kg^oC$

$m_1$ = mass of metal = x

$m_2$ = mass of coffee = 0.3 kg

$T_f$ = final temperature of aluminum metal= $110^oC$

$T_1$ = initial temperature of aluminum metal = $-10^oC$

$T_2$ = initial temperature of coffee= $140^oC$

Now put all the given values in the above formula, we get

$x* 900 J/kg^oC* (110-(-10))^oC=-(0.3 kg* 4000 J/kg^oC* (110-140)^oC$

$x=0.333 kg$

Mass of aluminum cubes = 0.3333 kg = 333.3 g

If mass of 1 cube is 1 gram, then numbers of cubes in 333.3 grams will be:

$=(333.3 g)/(1 g)=333.3\approx 330$

330 cubes of aluminum cubes will be required.

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Be sure to answer all parts. A baseball pitcher's fastballs have been clocked at about 97 mph (1 mile = 1609 m). (a) Calculate the wavelength of a 0.148−kg baseball (in nm) at this speed. × 10 nm (Enter your answer in scientific notation) (b) What is the wavelength of a hydrogen atom at the same speed? nm

Answers

Answer:

a) The wavelength of the baseball is $1.033* 10^(-25) nm$ .

b) 9.131 nm is the wavelength of a hydrogen atom at the 43.35 m/s.

Explanation:

Velocity of the baseball = v = 97 mile/hour

1 mile = 1609 meter

1 hour = 3600 seconds

$v =(97* 1609 m)/(3600 s)=43.35 m/s$

Mass of baseball = m = 0.148 kg

Wavelength of the baseball: $\lambda$

$\lambda =(h)/(mv)$ De Broglie wavelength

h =Planck's constant

$=(6.626* 10^(-34) Js)/(0.148 kg* 43.35 m/s)$

$\lambda =1.033* 10^(-34) m$

$1 m=10^9 nm$

$\lambda = 1.033* 10^(-25) nm$

The wavelength of the baseball is $1.033* 10^(-25) nm$ .

Mass of the hydrogen atom = $m=1.674* 10^(-27) kg$

Velocity of hydrogen atom = u = 43.35 m/s

$\lambda =(h)/(mv)$ De Broglie wavelength

$=(6.626* 10^(-34) Js)/(1.674* 10^(-27) kg* 43.35 m/s)$

$\lambda =9.131* 10^(-9) m$

$1 m=10^9 nm$

$\lambda =9.131 nm$

9.131 nm is the wavelength of a hydrogen atom at the 43.35 m/s.

Final answer:

To calculate the wavelength of the baseball and hydrogen atom, we can use the wavelength formula. However, the wavelengths calculated are extremely small and cannot be practically detected.

Explanation:

To calculate the wavelength of the baseball, we can use the wavelength formula: λ = v/f. In this case, the velocity (v) of the baseball is given as 97 mph, which is equal to 97 * 1609 m/h. The frequency (f) can be calculated by dividing the speed of light (3 * 10^8 m/s) by the wavelength of the baseball.

For the hydrogen atom, we can use the same formula. However, we need to convert the hydrogen atom velocity to m/s. Once we have the velocity in m/s, we can calculate the wavelength by dividing the velocity by the frequency.

It is important to note that the wavelength calculated for the baseball and hydrogen atom are extremely small and cannot be practically detected by our senses or instruments.

Learn more about Wavelength calculation here:

brainly.com/question/34184937

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As the speed of the particles decreases, -a. Intermolecular forces become stronger

b. Intermolecular forces become weaker

c. Intermolecular forces do not change

d. Energy increases
Engshus
ratoway

Answers

As the speed of the particles decreases, intermolecular forces become stronger. Thus, the correct option for this question is A.

What are Intermolecular forces?

The intermolecular forces may be defined as the forces of attraction. that is present between atoms, molecules, and ions when they are placed close to each other in order to form a compound or element. This force is continuously acting on the neighboring particles of different molecules.

It is found that at low temperature, when the speed of molecules/particles decrease, they migrate closer to one another that results in their intermolecular forces that become stronger as compared to the initial one.

As the attraction between molecules gradually increases, their movement decreases, and undergo fewer collisions between them.

Therefore, as the speed of the particles decreases, intermolecular forces become stronger. Thus, the correct option for this question is A.

To learn more about Intermolecular forces, refer to the link:

brainly.com/question/13588164

#SPJ2

Answer:

Explanation:

A solution of salt and water is 33.0% salt by mass and has a density of 1.50 g/ml. what mass of the salt in grams is in 5.00l of this solution?

Answers

To answer this item, we solve first for the mass of the solution by multiplying the density by the volume. That is,

m = (density)(volume)

Substituting the known values,
m = (1.50 g/mL)(5L)(1000 mL/1L)
m = 7500 grams

To determine the mass of the salt in the solution, multiply the calculated mass of the solution by the decimal equivalent of the percent salt in the solution.

m of salt = (7500 g)(0.33)
m of salt = 2475 grams

Answer: 2475 grams

To completely neutralize a 0.325 g sample of pure aspirin, 15.50 mL of a sodium hydroxide solution is added. If 16.25 mL of the same sodium hydroxide solution must be added to an aspirin tablet sample during a titration to reach the endpoint, calculate the mass of aspirin in the tableA. 0.310 g
B. 0.288 g
C. 0.392 g
D. 0.450 g
E. 0.341 g

Answers

Answer: The correct option is E.

Explanation: The reaction between aspirin (also known as acetylsalicylic acid) and sodium hydroxide is known as acid-base titration reaction.

By applying Unitary method, we get:

15.50mL of NaOH dissolves = 0.325 g of aspirin

So, 16.25 mL of NaOH will dissolve = $(0.325g)/(15.5mL)* 16.25mL$ = 0.341 g

Hence, the correct option is E.

Calculate the concentration of OH in a solution that contains 3910-4 M H30 at 25°C. Identify the solution as acidic, basic or neutral OA) 2.6 10-11 M, acidic OB)26 10-11 M. basic O c) 3.9 x 10-4 M, neutral OD) 2.7 * 10-2 M

Answers

Answer : The correct option is, (A) $2.6* 10^(-11)M$ , acidic

Explanation:

pH : It is defined as the negative logarithm of hydrogen ion or hydronium ion concentration.

When the value of pH is less then 7 then the solution will be acidic.

When the value of pH is more then 7 then the solution will be basic.

When the value of pH is equal to 7 then the solution will be neutral.

First we have to calculate the pH.

$pH=-\log [H^+]$

$pH=-\log (3.9* 10^(-4))$

$pH=3.41$

Now we have to calculate the pOH.

$pH+pOH=14\n\npOH=14-pH\n\npOH=14-3.41=10.59$

Now we have to calculate the $OH^-$ concentration.

$pOH=-\log [OH^-]$

$10.59=-\log [OH^-]$

$[OH^-]=2.6* 10^(-11)M$

Therefore, the $OH^-$ concentration is, $2.6* 10^(-11)M$

The maximum allowable concentrationof lead in drinking water is 9.0 ppb. If 2.0
X 10 grams of lead is present in 250
mL of water, is it safe to drink the water?
Support your answer with mathematical
proof.

Answers

We are given:

Maximum concentration of Lead in water = 9 ppb

Mass of Lead in the given solution = 20 grams

Volume of water in the given solution = 250 mL

What is 1 ppb?

1 ppb, short for parts-per-billion. As from its name itself, ppb is used to find how many molecules of solute are present per 1 Billion molecules of the solvent

you can also use it in grams to get the formula:

1 ppb = 1 gram of solute / 1 Billion grams of Solvent

Finding the Ideal ppb concentration:

We are given that the maximum allowed concentration is 9 ppb

which means that we need 9 grams of the solute per 1 Billion grams of Solvent: 9 grams of Solute / 10⁹ grams of Solvent

ppb Concentration of the given solution:

We have 20 grams of Solute in 250 mL of water

Since the density of water is 1 gram/mL

20 grams of Solute / 250 grams of Solvent

As we can see, this fraction is FAR more large that the maximum ppb concentration

This means that the concentration of Lead in the Given solution is higher than the maximum amount and Hence, is unfit to drink

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