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antiseptic1488 [7]
3 years ago
12

Quan used a beaker to prepare a solution consisting of 4 g of a reddish powder and 35 g of alcohol. As soon as the substances mi

xed together, he covered the beaker tightly so that no gas could escape. After the powder dissolved, he noticed a black solid fell to the bottom of the test tube. As part of his observation, he weighed the solution with the black solid. What did he find?
Chemistry
1 answer:
dybincka [34]3 years ago
4 0

Answer:

  • <em>That the total mass of the final solution with the black solid, inside the covered beaker, was equal to 39 g.</em>

<em />

Explanation:

The formation of a <em>black solid</em> that <em>fell to the bottom</em> of the test tube is the indication of a chemical reaction: the <em>4 g of reddish powder</em> and the <em>35 g of alcohol</em> reacted with each other and formed new substances.

The chemical reactions obey the law of conservation of mass: the mass of the reactants is equal to the mass of the products.

Since the beaker was tightly covered, none of the substances escaped, and all the products are present inside the beaker along with the reactants that were left over, in case some of them did not react to completion.

Therefore, the mass of the content of the beaker, after reaction, must be equal to the mass of the initial substances: 4 g  + 35 g = 39g.

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Charcoal from the dwelling level of the Lascaux Cave in France gives an average count of 0.97 disintegrations of ^14 C per minut
Verdich [7]

Answer:

Explanation:

count given by old sample = .97 disintegrations per minute per gram

count given by fresh sample = 6.68 disintegrations per minute per gram

Half life of radioactive carbon = 5568 years

rate of disintegration

dN / dt = λ N

In other words rate of disintegration is proportional to no of radioactive atoms present . As number reduces rate also reduces .

Let initial no of radioactive be N₀ and after time t , number reduces to N

N₀ / N = 6.68 / .97

Now

N=N_0e^{-\lambda t}

\frac{N}{N_0} =e^{-\lambda t}

\frac{6.68}{.97} = e^{\lambda t}

λ is disintegration constant

λ = .693 / half life

= .693 / 5568

= .00012446 year⁻¹

Putting the values in the equation above

\frac{6.68}{.97} = e^{.00012446\times t}

6.8866 = e^{.00012446\times t}

1.929577 = .00012446 t

t = 15503.6 years .  

4 0
3 years ago
Which type of van der walls force is responsible for holding polar molecules together? london dispersion dipole-dipole hydrogen
svet-max [94.6K]

Answer:

dipole-dipole

Explanation:

Polar molecules are formed as result of covalent bonds between atoms.

Dipole-dipole attraction are intermolecular bonds. Both London dispersion forces and dipole-dipole attraction are van der waals forces.

In dipole-dipole attraction, polar molecules (unsymmetrical molecules) line up such that the positive pole of one molecule attracts the negative pole of another. Example of such is found in HCl.

4 0
3 years ago
Calculate the pH of a solution that has [H3O+]=4.3 x 10^-5 M
Neko [114]

Answer:

pH = 4.4

Explanation:

pH = -log[H₃O⁺]

     = -log(4.3 × 10⁻⁵)

pH = 4.37 = 4.4

I'm actually learning this in my chemistry class right now lol. Hope this helps though. :)

6 0
3 years ago
How many grams of carbon dioxide will be produced if 76.4 grams of
goldfiish [28.3K]

Answer:

Assuming that all of the oxygen is used up, 1.53×4111.53×411 or 0.556 moles of C2H3Br3 are required. Because there are only 0.286 moles of C2H3Br3 available, C2H3Br3 is the limiting reagent.

Limiting Reagent What is the limiting reagent if 76.4 grams of C2H3Br3 were reacted with 49.1 grams of O2? C2H3Br3 + 11O2 → 8CO2 + 6H2O + 6Br2 SOLUTION Using Approach 1: A. 76.4g &times; (1 mol/ 266.72 g) = 0.286 moles C2H3Br3 49.1g &times; (1 mole/ 32 g) = 1.53 moles O2 B.

Explanation:

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https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Map%3A_Introductory_Chemistry_(Tro)/08%3A_Quantities_in_Chemical_Reactions/8.04%3A_Limiting_Reactant_and_Theoretical_Yield

5 0
3 years ago
What is required in order to melt a network solid?
mina [271]

Answer: In order to melt a network solid, a relatively large amount of heat is needed, sufficient to break the covalent bonds that hold the entire solid together

hope this helps

3 0
3 years ago
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