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Chemistry

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My name is Ann [436]3 years ago

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Henry Moseley organized the periodic table by A. atomic weight. B. atomic number. C. electronegativity. D. overall charge of ato

Leni [432]

B - Atomic number. Dmitri Mendeleev organised the table according to atomic weight, however this caused problems with elements such as iodine and tellurium, Iodine has a higher mass, but a lower atomic number. And to make iodine in the same group as similar elements (halogens), Mendeleev had to break his own rules and put it before tellurium in the table. Moseley fixed this problem by ordering the elements according to atomic (proton) number.

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3 years ago

Read 2 more answers

When planning a simple experiment, what does it mean to “test one variable”?

SSSSS [86.1K]

Answer:

I believe the answer is "b". "During the experiment, the scientist has only one element, or variable, that is changed to test the hypothesis."

Explanation:

I remember from last year but I'm not totally sure. Good luck!

3 0

3 years ago

25.0cm3 of s saturated potassium hydroxide is neutralized by 35.0cm3 of hydrogen chloride acid of concentration 0.75 mol/dm3. Ca

Kamila [148]

Answer:

Concentration of the original $\rm KOH$ solution: approximately $1.05\; \rm mol \cdot dm^{-3}$ .

Explanation:

Notice that the concentration of the $\rm HCl$ solution is in the unit $\rm mol\cdot dm^{-3}$ . However, the unit of the two volumes is $\rm cm^{3}$ . Convert the unit of the two volumes to $\rm dm^{3}$ to match the unit of concentration.

$\begin{aligned} V(\mathrm{NaOH}) &= 25.0\; \rm cm^{3} \\ &= 25.0\; \rm cm^{3} \times \frac{1\; \rm dm^{3}}{1000\; \rm cm^{3}} \approx 0.0250\; \rm dm^{3} \end{aligned}$ .

$\begin{aligned} V(\mathrm{HCl}) &= 35.0\; \rm cm^{3} \\ &= 35.0\; \rm cm^{3} \times \frac{1\; \rm dm^{3}}{1000\; \rm cm^{3}} \approx 0.0350\; \rm dm^{3} \end{aligned}$ .

Calculate the number of moles of $\rm HCl$ molecules in that $0.0350\; \rm dm^{3}$ of $0.75\; \rm mol \cdot dm^{3}$ $\rm HCl\!$ solution:

$\begin{aligned}n(\mathrm{HCl}) &= c(\mathrm{HCl}) \cdot V(\mathrm{HCl}) \\ &= 0.00350\; \rm dm^{3} \times 0.75\; \rm mol \cdot dm^{3} \\ &\approx 0.02625\; \rm mol\end{aligned}$ .

$\rm HCl$ is a monoprotic acid. In other words, each $\rm HCl\!$ would release up to one proton $\rm H^{+}$ .

On the other hand, $\rm KOH$ is a monoprotic base. Each $\rm KOH\!$ formula unit would react with up to one $\rm H^{+}$ .

Hence, $\rm HCl$ molecules and $\rm KOH\!$ formula units would react at a one-to-one ratio.

${\rm HCl}\, (aq) + {\rm NaOH}\, (aq) \to {\rm NaCl}\, (aq) + {\rm H_2O}\, (l)$ .

Therefore, that $0.02625\; \rm mol$ of $\rm HCl$ molecules would neutralize exactly the same number of $\rm NaOH$ formula units. That is: $n(\mathrm{NaOH}) = 0.02625\; \rm mol$ .

Calculate the concentration of a $\rm NaOH$ solution where $V(\mathrm{NaOH}) = 0.0250\; \rm dm^{3}$ and $n(\mathrm{NaOH}) = 0.02625\; \rm mol$ :

$\begin{aligned}c(\mathrm{NaOH}) &= \frac{n(\mathrm{NaOH})}{V(\mathrm{NaOH})} \\ &= \frac{0.02625\; \rm mol}{0.0250\; \rm dm^{3}}\approx 1.05\; \rm mol \cdot dm^{-3}\end{aligned}$ .

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3 years ago

How much heat is required to change 100 g of ice (H2O) at 253 K to vapor (steam) at 393 K?

soldier1979 [14.2K]

<u>Answer:</u> The heat required will be 58.604 kJ.

<u>Explanation: </u>

To calculate the amount of heat required, we use the formula:

$Q= m\times c\times \Delta T$

Q= heat gained or absorbed = ? J

m = mass of the substance = 100 g

c = heat capacity of water = 4.186 J/g ° C

Putting values in above equation, we get:

$\Delta T={\text{Change in temperature}}=(393-253)K=140K=140^oC$

$Q=100g\times 4.186J/g^oC\times 140^oC$

Q = 58604 Joules = 58.604 kJ (Conversion factor: 1 kJ = 1000J)

Thus, heat released by 100 grams of ice is 58.604kJ.

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4 years ago

The quantity of energy released or absorbed as heat during a chemical reaction is called the 28. a. temperature. c. entropy d. f

Tatiana [17]

Answer: enthalpy of reaction.

Explanation:

Temperature of the gas is defined as the degree of hotness or coldness of a body. It is expressed in units like $^0C$ and $K$

Entropy is the measure of randomness or disorder of a system. If a system moves from an ordered arrangement to a disordered arrangement, the entropy is said to decrease and vice versa.

Free energy is the amount of energy that can be converted into useful work.

Enthalpy of the reaction is the difference between the energy of products and the energy of reactants. it is either the heat released or absorbed during the reaction. It is either positive or negative.

5 0

4 years ago