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3 years ago

Need help, please. :)

Chemistry

1 answer:

wolverine [178]3 years ago

6 0

A change of one unit on the pH scale represents a change in the concentration of hydrogen ions by a factor of 10, a change in two units represents a change in the concentration of hydrogen ions by a factor of 100. Thus, small changes in pH represent large changes in the concentrations of hydrogen ions.

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Which statement about the elements in the periodic table is true

egoroff_w [7]

A. The number of valence electrons increases as atomic mass increases. == Generally true for the representative elements since atomic mass generally increases with increasing Z.

B. The reactivity of alkali metals increases as atomic mass increases. == True. Atomic mass increases down the column and so does reactivity

C. The reactivity of the halogens increases as atomic mass increases. == False. Reactivity decreases down the column.

D. The number of valence electrons decreases across a period. == False. In general, the number of valence electrons increases across a period, particularly for the representative elements.

6 0

3 years ago

Read 2 more answers

Identify from the following list of molecules and ions which behave as Lewis acids: CO2, NH3, BCl3, Fe3+. (A) CO2 and NH3 (B) NH

Anettt [7]

Answer : The correct option is, (D) CO₂, BCl₃, and Fe³⁺

Explanation :

According to the Lewis concept, an acid is defined as a substance that accepts electron pairs and base is defined as a substance which donates electron pairs.

(a) $CO_2$

It is a Lewis-acid because it can accepts electron pairs.

(b) $NH_3$

It is not a Lewis-acid because it can not accepts electron pairs but it is a base because it can donates and accept hydrogen ion.

(c) $BCl_3$

It is a Lewis-acid because it can accepts electron pairs because it has an incomplete octet and an empty 2p orbital.

(d) $Fe^{3+}$

It is a Lewis-acid because it can accepts electron pairs.

Hence, the ions which behave as Lewis acids are, CO₂, BCl₃, and Fe³⁺

6 0

3 years ago

Determine whether or not each mixture is a buffer. check all that apply. check all that apply. koh and nh3 hbr and nacl hcl and

erastova [34]

A buffer is usually composed of either:
- a weak base combined with its conjugate acid, or
- a weak acid combined with its conjugate base

Now, examining each of the choices:
1- KOH and NH3: since they are both bases, thus this mixture is not a buffer
2- HBr and NaCl: since HBr is a strong acid while NaCl is the salt of another different acid, thus this mixture is not a buffer
3- HCl and HBr: these are both considered to be strong acid, thus this mixture is not a buffer
4- HCHO2 and NaCHO2: as for HCH02, it is considered a weak base while NaCHO2 is considered its conjugate base, thus this mixture is a buffer

3 0

3 years ago

What is the energy of light associated with a transition from n=3 to n=8 in a hydrogen atom? Does this represent absorption or e

solong [7]

Explanation:

Energy levels to be n = 8 and n = 3. Rydberg's equation will allow you calculate the wavelength of the photon emitted by the electron during this transition

1λ = R ⋅ (1/nf^2 − 1/ni^2)

where,

λ - the wavelength of the emitted photon

R - Rydberg's constant = 1.0974 x 10^7m

nf - the final energy = 8

ni - the initial energy level = 3

1/λ = 1.0974 x 10^7 * (1/8^2 − 1/3^2)

= -1.05x 10^6 m.

Using Heinsberg's equation,

E = (h * c)/λ

Calculating the energy of this transition you'll have to multiply Rydberg's equation by h * c

where,

h - Planck's constant = 6.626 x 10^−34 Js

c - the speed of light = 3.0 x 10^8 m/s

So, the transition energy, E = (6.626 x 10^−34 * 3 x 10^8) * -1.05x 10^6

= -2.08 x 10^-19 J.

When an electron transitions from a less excited state to a excited state (higher energy orbit), the difference in energy is absorbed as a photon.

The energy is negative which means energy is lost or dissipated to the surroundings. Therefore, an absorption of photons.

8 0

3 years ago

Tris base has a molecular weight of 121 g/mol. How many grams of tris base would you need to make 250ml of a 200mM SOLUTION

STatiana [176]

Answer:

6.05 g

Explanation:

Molarity of a substance , is the number of moles present in a liter of solution .

M = n / V

M = molarity

V = volume of solution in liter ,

n = moles of solute ,

From the question ,

M = 200mM

Since,

1 mM = 10⁻³ M

M = 200 * 10⁻³ M

V = 250 mL

Since,

1 mL = 10⁻³ L

V = 250 * 10⁻³ L

The moles can be calculated , by using the above relation,

M = n / V

Putting the respective values ,

200 * 10⁻³ M = n / 250 * 10⁻³ L

n = 0.05 mol

Moles is denoted by given mass divided by the molecular mass ,

Hence ,

n = w / m

n = moles ,

w = given mass ,

m = molecular mass .

From the question ,

m = 121 g/mol

n = 0.05 mol ( calculated above )

The mass of tri base can be calculated by using the above equation ,

n = w / m

Putting the respective values ,

0.05 mol = w / 121 g/mol

w = 0.05 mol * 121 g/mol

w = 6.05 g

3 0

3 years ago

Read 2 more answers