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Some science questions pleaseeee help

Free_Kalibri [48]

The answers is c! !!!!!!!

4 0

3 years ago

Read 2 more answers

6. Alex wanted to find out what toothpaste made teeth the cleanest. Everyday she brushed her

vichka [17]

Answer:

a) Independent variable (IV): toothpase brand

b) Dependent variable (DV): amount of plaque left

c) Control: water

d) Constants: amount of toothpaste, kind of toothbrush, how long the toothbrushing took.

Explanation:

In an experiment there usually be independent variable, dependent variable, control gropus, and constants.

The independendent variable is the variable whose impacts on other varbiale. Then, the independent variable is manipulated or changed by the scientist (the person that designs or perform the experiment).

In this case, Alex is changing the brand of toothpaste: Crest, Colgate, and Close-Up. So the answer to the first question is brand of toothpaste:

a. Independent variable (IV): toothpaste brand.

The dependent variable is the variable that changes by the effect of changing the independent variable. It is the variable whose behavior you want to explain in terms of the independent variable.

In this case, Alex wants to determine the effect of the toothtpaste brand on the plaque, so the dependent variable is how much plaque is left.

b. Dependent variable (DV): how much plaque is left.

The control is a group of experiments used for comparison. This is, you do not include the independent variable in them. In this example it is the set of experiments made with only water. The scientist will be able to compare the results of using toothpase with no using toothpaste on the plaque when he includes a group of experiments where no toothpaste is used but water.

c. Control: water

In order to state if it is the change in the independent variable what causes or explains the results on the dependent variable, the scientist must make sure that no other changes occur during the experimentation.

In this case, it is not stated which other conditions Alex made sure to remain constant, but for sure they should include the amount of toothpaste used, the kind of teethbrush, and the time of brushing.

d. Constants: presumably, the amount of toothpase, the kind of toothbrush, and the time of brushing.

3 0

3 years ago

xavier, yaozhou and zara had some beads. xavier and yaozhou had total of 438 beads. xavier and zara had total of 204 beads. youz

SVEN [57.7K]

To solve this problem, we need to set-up algebraic expression. First, use variables to represent the number of beads.

Let: x = number of Xavier's beads
y = number of Yaozhou's beads
z = number of Zara's beads

It is important to note that since we have three unknowns, we should also have three independent equations. Based on the given statements, we have the following three equations:

(1) x + y = 438
(2) x + z = 204
(3) y = 3z

Substitute y in terms of z in equation (1). Then multiply equation (2) with -1.

x + 3z = 438
-(x + z = 204)
-------------------
2z = 234
z = 117

From equation (3),

y = 3(117) = 351

Using equation (1),

x = 438 - 351 = 87

Thus, Xavier had 87 beads.

5 0

3 years ago

What is the boiling point of a solution made by adding 6.69 g of magnesium chloride to 250.0 g of water?. Use the formula of the

olya-2409 [2.1K]

Answer:

100.432ºC

Explanation:

Ebullioscopy is the elevation of the boiling point of a solvent that has a solute nonvolatile dissolved. The change in the temperature may be calculated by Raoult's law:

ΔT = Kb.W.i

Where ΔT is the temperature change, Kb is the ebullioscopy constant, W is the molality and i is the Van't Hoff factor, which determinates the particles that affect the proper.

The molality is:

W = m1/(M1xm2)

Where m1 is the solute mass (in g), M1 is the molar mass of the solute, and m2 is the mass of the solvent (in kg).

The Van't Hoff factor is the number of final particles divided by the number of initial particles. Magnesium is from froup 2, so it forms the cation Mg⁺², and chlorine ins from group 7 and forms the anion Cl⁻, the salt is MgCl₂ and dissociates:

MgCl₂ → Mg⁺²(aq) + 2Cl⁻(aq)

So, it has 1 particle in initial, and 3 in final (1 Mg⁺² and 2 Cl⁻). So:

i = 3/1 = 3.

The molar mass of MgCl₂ is: 24.3 + 2x35.5 = 95.3 g/mol, m1 = 6.69g, m2 = 0.250 kg, so:

W = 6.69/(95.3x0.250)

W = 0.281 m

Then:

ΔT = 0.512x0.281x3

ΔT = 0.432ºC

The normal boling point of water is 100ºC, so

T - 100 = 0.432

T = 100.432ºC

6 0

3 years ago

The density of ethanol, C2H5OH, is 0.789 g/mL. How many milliliters of ethanol are needed to produce 15.0 g of CO2 via a combust

bearhunter [10]

The answer is 9.94 ml.

<h3>What is density?</h3>

Density is a word we use to describe how much space an object or substance takes up (its volume) in relation to the amount of matter in that object or substance (its mass).
Another way to put it is that density is the amount of mass per unit of volume. If an object is heavy and compact, it has a high density.

Given,

The density of ethanol, C2H5OH = 0.789 g/mL

$n (CO_{2} ) = \frac{m}{M} = \frac{15G}{44 g/mol} } = 0.341 mol;$

$n ( C_{2} H_{2} OH) = \frac{n (CO_{2}) }{2} = \frac{0.341}{2} = 0.1705 mol;$

$m (C_{2} H_{2} OH) = 0.1705 mol * 46 g/ mol$ = 7.843 g

$V (C_{2} H_{2} OH ) = \frac{7.843}{0.789} = 9.94 ml.$

Therefore, the answer is 9.94 ml

Learn more about density of ethanol,

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The complete question is -

If the density of ethanol, C2H5OH, is 0.789 g/mL. How many milliliters of ethanol are needed to produce 15.0 g of CO2 according to the following chemical equation?

C2H5OH(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(l)

5 0

2 years ago