Which scientist was the first to propose the hellocentric model of the universe?

Chemistry

1 answer:

Westkost [7]3 years ago

6 0

Nicolaus Copernicus

Nicolaus Copernicus in his De revolutionibus orbium coelestium ("On the revolution of heavenly spheres", first printed in 1543 in Nuremberg), presented a discussion of a heliocentric model of the universe in much the same way as Ptolemy in the 2nd century had presented his geocentric model in his Almagest.

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How many grams of methionine (MW = 149.21) are needed to make 20 mL of a 150 mM solution?

Leni [432]

Answer:

0.45 g

Explanation:

Step 1: Given data

Molar mass of methionine (M): 149.21 g/mol

Volume of the solution (V): 20 mL

Concentration of the solution (C): 150 mM

Step 2: Calculate the moles of methionine (n)

We will use the following expression.

n = C × V

n = 150 × 10⁻³ mol/L × 20 × 10⁻³ L

n = 3.0 × 10⁻³ mol

Step 3: Calculate the mass of methionine (m)

We will use the following expression.

m = n × M

m = 3.0 × 10⁻³ mol × 149.21 g/mol

m = 0.45 g

7 0

3 years ago

Draw the lewis structure of the hypochlorite ion clo- . include lone pairs

Dmitry_Shevchenko [17]

Solution:- Hypochlorite ion $ClO^-$ has one Cl and one O atom. Cl has 7 valence electrons and O has 6 valence electrons. Since there is one negative charge on the ion,

total valence electrons = 7 + 6 +1 = 14

(note:- if there is negative charge then it is added and if there is positive charge then it is subtracted while calculating the valence electrons)

Both Cl and O atoms wants to complete their octet and so for this we put a single bond between them. Single bond means two electrons, so the remaining electrons would be 14 - 2 = 12

It means 12 electrons will be placed as lone pair of electrons. To complete the octet, we put 6 dots around each of the atom. Oxygen is more electron negative than Cl, so we show the -1 charge for oxygen.